Deep Dark Fudge Cake Recipe

Prepare

Preheat oven to 350°F (175°C). Grease and line an 8- or 9-inch round cake pan (or two 8-inch pans for layered cake) with parchment and lightly grease the parchment.

Mix dry ingredients

In a large bowl, whisk together the all-purpose flour, unsweetened cocoa powder, granulated sugar, brown sugar, baking powder, baking soda, and salt until evenly combined and no lumps of cocoa remain.

Combine wet ingredients

In a separate medium bowl or large measuring cup, whisk the eggs, buttermilk, vegetable oil, and vanilla until smooth.

Combine wet + dry

Make a well in the dry ingredients and pour in the wet mixture. Stir gently with a spatula or wooden spoon just until combined and no large streaks of flour remain. Do not overmix.

Add hot coffee

Pour the hot brewed coffee (or hot water) into the batter and stir until smooth. The batter will be thin — this produces a very fudgy, moist crumb. Scrape the batter into the prepared pan(s) and smooth the top.

Bake

Bake in the center of the preheated oven for 28–35 minutes for an 8- or 9-inch cake (or 22–28 minutes for two 8-inch pans), until a toothpick inserted in the center comes out with a few moist crumbs but not raw batter. Rotate the pan halfway through baking for even browning.

Cool

Allow the cake to cool in the pan on a wire rack for 10–15 minutes, then run a knife around the edge and invert onto the rack to cool completely before frosting. For layered cake, cool completely, level layers as needed, then frost.

Melt butter

In a medium saucepan over low heat, melt the unsalted butter until fully melted but not browned.

Whisk in cocoa

Remove the pan from heat and whisk in the cocoa powder until smooth and lump-free.

Add sugar and liquids

Return the pan to very low heat. Add the confectioners' sugar in two additions, alternating with the milk, whisking to incorporate after each addition. Add the corn syrup (or honey), vanilla extract, and salt. If the frosting is too thick, add additional milk 1 teaspoon at a time until it reaches a thick but spreadable consistency; if too thin, add a bit more powdered sugar.

Cool slightly

Allow the frosting to cool 5–10 minutes so it thickens slightly. Stir often to keep it glossy.

Frost the cake

Place the cooled cake on a serving plate. Using a spatula or offset spatula, spread a thin crumb coat of frosting over the top and sides. Chill 10 minutes if needed, then apply a final generous layer of fudge frosting, smoothing or creating swirls as desired.

Finish

If using, sprinkle dark chocolate shavings and a few sea salt flakes on top. Let the frosting set about 20–30 minutes at room temperature before slicing for clean cuts. Store covered at room temperature for 1–2 days or refrigerate up to 5 days (bring to room temperature before serving).

For a more dramatic presentation, shave a bar of dark chocolate over the cake, scatter cocoa nibs, or lightly dust with additional cocoa powder. If you like contrast, sprinkle the sea salt flakes just before serving.