Ingredients for the Chocolate Cake

• 1 ¾ cups granulated sugar
• ¾ cup unsalted butter, softened
• 1 cup powdered sugar
• 6 large eggs
• 2 teaspoons pure vanilla extract
• 2 cups all-purpose flour
• ¾ cup unsweetened cocoa powder
• 2 cups finely chopped walnuts or pecans
• ½ teaspoon salt
• 1 teaspoon baking powder
• ½ cup whole milk
• ½ cup strong brewed coffee, cooled
• 1 cup semi-sweet chocolate chips

Ingredients for the Fudgy Tunnel Filling

• 1 cup semi-sweet chocolate chips
• ½ cup heavy cream
• 2 tablespoons unsalted butter
• 2 tablespoons powdered sugar
• 1 teaspoon pure vanilla extract
• ¼ teaspoon salt

Ingredients for the Chocolate Glaze

• 1 ½ cups powdered sugar
• ½ cup unsweetened cocoa powder
• 4 tablespoons unsalted butter
• ¼ cup whole milk
• 1 teaspoon pure vanilla extract
• Pinch of salt

Optional Ingredients for Decoration

• Chocolate shavings
• Mini chocolate chips
• Chopped toasted pecans
• Unsweetened cocoa powder
• Powdered sugar
• Small pieces of chocolate

Detailed Preparation and Baking Instructions

Preparing the Oven and Bundt Pan

Begin by preheating your oven to 350°F (175°C). Give the oven plenty of time to reach the correct temperature before the cake goes inside, because an evenly heated oven helps the cake rise and bake consistently.

Choose a sturdy 10- to 12-cup Bundt pan with a deep central tube and well-defined ridges. The shape of the pan is important because it creates the beautiful sculpted appearance seen in the finished cake.

Generously grease every part of the Bundt pan with softened butter or nonstick baking spray. Pay special attention to the deep grooves because those areas can make the cake stick if they are not properly coated.

Dust the greased pan lightly with cocoa powder instead of ordinary flour. Cocoa powder keeps the outside of the chocolate cake dark and prevents pale flour marks from appearing on the finished surface.

Tap the pan gently over the sink to remove excess cocoa powder. Set the prepared pan aside while you make the chocolate batter.

Preparing the Chocolate Cake Batter

Place the unsalted butter and granulated sugar into a large mixing bowl. Beat them together with an electric mixer until the mixture becomes pale, fluffy, and creamy.

Add the powdered sugar gradually while continuing to beat the butter mixture. Scrape the sides of the bowl occasionally so that all the ingredients become evenly incorporated.

Add the eggs one at a time. Beat well after each egg before adding the next one, allowing the mixture to become smooth and creamy.

Add the pure vanilla extract and mix it through the batter. Vanilla gives the chocolate cake a deeper, more rounded flavor rather than making it taste simply sweet.

In a separate bowl, combine the all-purpose flour, unsweetened cocoa powder, salt, and baking powder. Whisk the dry ingredients together thoroughly so the cocoa powder is evenly distributed.

Add approximately one-third of the dry ingredients to the butter mixture. Mix on low speed until the flour is just incorporated, being careful not to overmix the batter.

Pour in half of the whole milk and continue mixing gently. Alternating the dry ingredients with the milk helps create a smooth batter without making it excessively dense.

Add another portion of the dry ingredients followed by the remaining milk. Continue mixing gently until everything begins to come together.

Pour in the cooled strong brewed coffee. Coffee intensifies the flavor of chocolate without making the finished cake taste strongly like coffee.

Mix the batter just until the coffee has been incorporated. Avoid prolonged mixing because excessive gluten development can make the cake tougher.

Fold the finely chopped walnuts or pecans into the batter using a large rubber spatula. The nuts provide texture and are especially traditional in this style of chocolate cake.

Add the semi-sweet chocolate chips and fold them gently through the mixture. These melted pockets of chocolate will add extra richness to the cake.

The finished batter should be thick, glossy, and deeply chocolate-colored. It should slowly fall from the spatula rather than running like a thin cake batter.

Creating the Fudgy Chocolate Center

Place the semi-sweet chocolate chips into a heatproof bowl. The chocolate should be finely chopped if you are using large pieces so that it melts evenly.

Heat the heavy cream in a small saucepan over medium-low heat until it becomes hot and begins producing gentle steam. Do not allow the cream to boil aggressively.

Pour the hot cream over the chocolate chips. Let the mixture sit undisturbed for several minutes so the heat can soften the chocolate.

Add the unsalted butter and stir slowly from the center outward. Continue stirring until the chocolate becomes completely smooth and glossy.

Add the powdered sugar, pure vanilla extract, and salt. Stir until the filling is thick, shiny, and completely homogeneous.

Allow the chocolate filling to cool for several minutes. It should become thick enough to sit inside the cake rather than immediately spreading everywhere.

Filling the Bundt Pan

Spoon approximately half of the chocolate cake batter into the prepared Bundt pan. Spread it carefully around the pan, making sure the batter reaches the bottom of the ridges.

Use the back of a spoon to create a shallow channel around the center of the batter. Keep the channel away from the outer and inner walls of the pan so the filling remains enclosed inside the cake.

Spoon the fudgy chocolate filling into the channel. Try to keep the filling concentrated in the middle rather than allowing it to touch the sides of the Bundt pan.

Cover the chocolate filling with the remaining cake batter. Gently spread the batter over the filling until it is completely enclosed.

Run a spatula around the top of the batter to make the surface reasonably even. Do not press aggressively because you do not want to push the fudgy filling toward the edges.

Tap the Bundt pan gently on a folded kitchen towel. This helps remove large air pockets and settles the batter into the intricate grooves of the pan.

Baking the Chocolate Cake

Place the Bundt pan on the center rack of the preheated oven. Keeping the pan centered allows hot air to circulate around it more evenly.

Bake the cake for approximately 45 to 55 minutes. Baking time can vary depending on the size and material of your Bundt pan.

Begin checking the cake near the 45-minute mark. The exterior should look set, while the center should still retain some moisture.

Insert a wooden skewer into the cake away from the fudgy filling. It should come out with moist chocolate crumbs rather than completely wet batter.

Do not test directly through the center tunnel because the fudgy filling is supposed to remain soft. A skewer entering the filling will naturally come out covered in chocolate.

When the cake is finished, remove it from the oven and place the pan on a cooling rack. Allow it to rest in the pan for approximately 15 to 20 minutes.

Carefully loosen the edges of the cake using a thin silicone spatula or butter knife. Work gently around the ridges so you do not tear the delicate chocolate crust.

Place a large serving plate upside down over the Bundt pan. Hold both the plate and pan securely, then carefully invert the cake.

Lift the Bundt pan slowly. If the cake has been properly greased and cooled, it should release cleanly and reveal its beautiful ridged shape.

Allow the cake to cool completely before applying the glaze. A hot cake will cause the glaze to melt excessively and may make the exterior appear thinner than intended.

Making the Glossy Chocolate Glaze

Place the unsalted butter and whole milk into a small saucepan. Warm them over low heat until the butter melts completely.

Remove the saucepan from the heat and whisk in the unsweetened cocoa powder. Keep stirring until the mixture becomes smooth and free of cocoa lumps.

Gradually add the powdered sugar while whisking continuously. Adding it slowly produces a smoother glaze and prevents large lumps from forming.

Add the pure vanilla extract and a small pinch of salt. The salt balances the sweetness and enhances the deep chocolate flavor.

If the glaze becomes too thick, add a teaspoon of milk at a time. If it becomes too thin, allow it to cool slightly before adding additional powdered sugar.

The finished glaze should be thick enough to coat the cake but fluid enough to slowly flow down the Bundt ridges.

Finishing the Tunnel of Fudge Cake

Place the completely cooled cake on a serving platter. Make sure the widest ridges are facing outward so the glaze can naturally cascade down the sides.

Spoon the chocolate glaze over the top of the cake. Allow it to move naturally over the ridges instead of trying to cover every section perfectly.

Continue adding glaze around the entire cake until you have a thick, glossy chocolate coating. The contrast between the dark cake and shiny glaze gives the dessert its dramatic appearance.

For an especially luxurious finish, sprinkle chocolate shavings over the glaze while it is still slightly soft. The shavings will adhere naturally to the surface.

Add a small amount of chopped toasted pecans if you want additional crunch and a more traditional nutty chocolate flavor.

Let the finished cake stand at room temperature for about 20 to 30 minutes. This allows the glaze to set slightly while keeping the interior wonderfully soft.

Slice the cake with a sharp, thin knife. Wipe the knife between cuts if you want especially clean slices that clearly reveal the fudgy center.

The first slice should expose the characteristic chocolate tunnel in the middle. The filling should look thick, moist, and almost truffle-like rather than completely liquid.

Serve each slice on its own or with a small scoop of vanilla ice cream. The cold, creamy ice cream provides a wonderful contrast to the rich chocolate cake.

For an even more indulgent presentation, drizzle a little extra warm chocolate sauce over each slice. A few fresh berries can also provide acidity that balances the richness.

The cake is best enjoyed slightly warm or at room temperature. If refrigerated, allow individual slices to sit at room temperature for a short while before serving.

Store leftover cake in an airtight container at room temperature for up to 2 days, provided your kitchen is not excessively warm. For longer storage, refrigerate it securely covered.

If refrigerated, the chocolate center will become firmer. You can gently warm an individual slice in the microwave for approximately 10 to 15 seconds to restore some of its soft fudgy texture.

For the most dramatic result, serve the cake shortly after slicing while the chocolate interior is soft. This creates the rich, molten-looking effect suggested by the cake in your image.

Final Result

You should end up with a deeply chocolatey Bundt cake featuring a tender, moist crumb, a rich hidden tunnel of chocolate fudge, and a glossy coating cascading down the ridges.

The combination of cocoa powder, melted chocolate, coffee, butter, and chocolate chips gives the cake a particularly intense chocolate flavor without relying on the filling alone.

For a spectacular dessert-table presentation, place the finished cake on a dark or neutral-colored platter and scatter a few chocolate shavings around the base. The glossy glaze will catch the light and emphasize the dramatic Bundt shape.

Prep time: about 30 minutes
Baking time: 45–55 minutes
Cooling time: about 1 hour
Servings: 12–16 slices
Oven temperature: 350°F (175°C)