• Preheat the oven to 350°F (175°C).
• Grease and line three 8-inch cake pans with parchment.

Vanilla Batter

• In a large bowl, whisk flour, baking powder, baking soda, and salt. Set aside.
• In a stand mixer, beat the butter for one minute. Add the sugar and beat for another 3 minutes at medium-high speed, until light and fluffy.
• Add eggs one at a time, beating well after each addition. Mix in the vanilla.
• Add the sour cream and mix.
• Add the flour mixture in 3 parts, alternating with the milk. As soon as the flour incorporates, stop mixing. Set the batter aside.

Chocolate Batter Swirl

• In another large bowl, mix the cocoa powder, hot coffee, sugar, and melted butter together.
• Add 1¾ cups of batter to the bowl.
• Mix with a whisk gently to combine.

Frosting

• Place the chopped chocolate in a heatproof bowl.
• Heat heavy cream in the microwave or in a small saucepan until steaming (not boiling).
• Pour over the chocolate and let sit 1–2 minutes.
• Stir until smooth and fully melted.
• Let it cool to room temperature until soft and spreadable, not warm. It should take about 20 to 30 minutes.
• Sift the cocoa powder and powdered sugar together. Set aside.
• Beat the butter on medium-high for 3–4 minutes until pale and fluffy.
• Add the sifted cocoa powder and powdered sugar to the butter in three additions, mixing on low after each.
• Increase to medium speed and whip for 1 minute.
• Add the cooled ganache and the vanilla in.
• Beat on medium-high for 2–3 minutes until smooth and fluffy.

To assemble

• I recommend weighing both batters and dividing the each number by three, so you have equal amounts in each pan.
• Pour about 1 cup of vanilla batter on the bottom of the prepared pan.
• Add spoonfuls of chocolate batter on top. Followed by more vanilla batter.
• Swirl with a knife once or twice to create a marble effect.

Bake

• Bake the cake layers in the preheated oven for 22–27 minutes. A toothpick should come out clean with a few moist crumbs.
• Cool in pans 10 minutes, then turn out onto racks to finish cooling completely.

To decorate

• Once the cake layers are completely cool, level them if needed. Place the first layer on a cake board or serving plate and spread an even layer of chocolate frosting on top. Add the second layer and repeat, then place the third layer on top. Apply a thin crumb coat around the cake and chill for 15–20 minutes until set.
• For the final coat, spread frosting around the sides and top using an offset spatula. To create the textured swirl pattern shown in the photo, hold a mini offset spatula at a slight angle against the side of the cake and keep it steady while slowly spinning the cake on a turntable. The motion of the turntable—rather than moving your hand—creates clean, even ridges. Repeat the same technique on the top of the cake: hold the spatula still and turn the cake to achieve a smooth, spiral finish.
• Once the frosting is smooth, fit a piping bag with a 4B piping tip and pipe swirls around the top edge of the cake. Finish by placing Lindt truffles (or your preferred chocolate truffles) on top of each swirl. Add chocolate shavings or curls if you want extra texture and detail.
• The cake is now ready to serve or chill until needed.