Step 1

Prep: Preheat oven to 350 F/177 C. Grease one 8-inch round cake pan with cooking spray or butter. Line the bottom of the pan with a piece of parchment paper, grease the parchment to prevent it from getting stuck to the cake and dust the pan with cocoa powder.

Step 2

Bloom cocoa: Pour hot coffee over cocoa powder. Set aside.

Step 3

Melt butter and chocolate: Melt butter in a small saucepan over low heat, add chopped chocolate and stir constantly until fully melted. Remove from heat and move to a large heat-proof mixing bowl.

Step 4

Make batter: Stir in sourdough discard, milk, sugars, oil and vanilla into the butter mixture. Beat eggs in one at a time. Sift flour, baking powder, baking soda and salt into the rest of the ingredients. Fold in the flour mixture. Pour the hot coffee and cocoa powder mixture into the batter (reheat the mixture if it has cooled down). Stir until just combined, do not over mix or your cake may turn out tough and rubbery.

Step 5

Bake: Pour the batter into the prepared cake pan. Tap the pan against your kitchen counter to pop air bubbles in the batter. Bake the cake for 40 to 45 minutes or until a toothpick inserted in the center of the cake comes out with only a few crumbs. Let the cake cool in the pan for 5 minutes, run an offset spatula around the edges of the cake before turning it out onto a cooling rack. Let the cake cool for at least 1 hour before frosting.

Step 6

Make the ganache: While your cake bakes, set a large heat-proof bowl over a small saucepan with an inch of simmering water. Heat heavy cream and chopped milk chocolate in the mixing bowl stirring occasionally until the chocolate is melted. Remove from heat and cover the ganache with plastic wrap (the plastic wrap should make contact with the ganache to prevent it from forming a skin). Allow the ganache to cool completely before proceeding.

Step 7

Make frosting: Fold the sour cream and powdered sugar into the cooled ganache. Using an electric mixer with a whisk attachment, whip the mixture until fluffy and appears lighter in color, about 2 to 3 minutes (don’t over whip or your frosting will seize and become grainy).

Step 8

Assemble the cake: Spread a generous layer of frosting on top of the cake, frost the sides or leave bare for a more rustic look. Sprinkle chocolate shavings or cocoa powder on top.

Step 9

Enjoy and store: Serve the cake immediately after frosting. Store any leftover slices in an airtight container in the refrigerator. The cake will become deliciously dense and fudgy as it cools. If you want to restore the cake’s spongy texture, let it come to room temperature before enjoying.