• Preheat oven to 350º F. Spray a 9 inch round cake pan with cooking spray and line the bottom with parchment paper. Set aside.

Make the cake.

• In a large bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
  1 cup all-purpose flour, 1 cup granulated sugar, ⅜ cup cocoa powder, 1 teaspoon baking powder, ¾ teaspoon baking soda, ½ teaspoon fine sea salt
• To the dry ingredients add milk, oil, sour cream, egg, and vanilla. Stir until well combined. The batter will be thick, similar to the texture of brownie batter.
  3 ounces whole milk, ¼ cup vegetable oil, 2 Tablespoons full-fat sour cream, 1 large egg,, 1 teaspoon vanilla extract
• Add hot coffee to the batter, carefully mixing with a whisk until well blended. The batter will now be very thin.
  ½ cup hot coffee
• Pour the batter into the prepared cake pan and bake for 30-35 minutes, or until the top sprigs back when gently poked and a cake tester inserted into the center of the cake comes out clean or with just a few moist crumbs. Let the cake cool completely in the pan on a wire rack.

Make the mousse.

• Place a small amount of water in the bottom of a double boiler (or a medium saucepan) and bring to a simmer. Place the bowl of the double boiler (or a medium heat-safe bowl) on top of the pan of simmering water, checking to make sure the bowl sits above and does not touch the water.
• In the bowl, combine the egg yolks, brewed coffee, 3 Tablespoons (37 grams) of the sugar, and salt. Cook the mixture, whisking constantly, until it becomes lighter in color and doubles in volume, about 5 minutes. An instant-read thermometer inserted into the mixture should read 160°F.
  6 large egg yolks, 3 ounces strong brewed coffee, 4 ½ Tablespoons granulated sugar, ⅛ teaspoon fine sea salt
• Remove the bowl from the pan of simmering water. Add the chocolate and whisk until the chocolate melts and the mixture is smooth. Let the mixture stand, whisking occasionally, until it cools to room temperature, about 30 minutes.
  9 ounces semisweet chocolate baking bar
• While the chocolate mixture cools, place the chocolate cake onto the base of a 9 inch springform pan. Place the band around the cake and close the clamp to secure it to the base. Set aside.
• In a large bowl, beat the egg whites using an electric hand mixer until they become foamy. With the mixer running on low speed, slowly add the remaining 1 ½ Tablespoons (19 grams) sugar to the foamy egg whites. Increase speed to high and beat the mixture until stiff peaks form.
  3 large egg whites
• Fold the whipped egg whites into the chocolate mixture, being careful not to deflate the mixture.
• In the same large bowl you used to whip the egg whites, beat heavy cream using an electric hand mixer until stiff peaks form.
  ¾ cup heavy whipping cream
• Gently fold the chilled whipped cream into the chocolate mixture just until blended, again being careful not to deflate the mixture.
• Spoon the mousse over the top of the cake. Use an offset spatula to spread the mousse to the sides and smooth the top. Chill the cake and mousse in the fridge for at least 3 hours.
• Once chilled, take the cake out of the fridge. Remove the band from the around the cake by first running an offset spatula around the edge of the cake between the mouse and the pan, then opening the clamp and lifting the band up off the cake.

Make the ganache.

• Add the chopped chocolate to a medium heat-safe bowl and set aside.
  6 ounces semisweet chocolate baking bar
• Add the cream to a small saucepan and heat until just shy of simmering.
  6 ounces heavy whipping cream
• Pour the warmed cream over the chocolate and let it sit for 2 minutes. Then stir with a rubber spatula until the chocolate is completely melted and the mixture is smooth and shiny.
• Let the ganache cool very briefly, just 2-3 minutes. It should thicken ever-so-slightly but still be pourable. Then pour the ganache over the mousse and use an offset spatula to spread the ganache over the top of the cake and just to the edges, allowing some of the ganache to drip down the sides of the cake.
• Return the cake to the fridge for 30 minutes to let the ganache set. Slice and serve chilled.