Preheat the Oven: Preheat your oven to 350°F (175°C) and prepare a cake pan by greasing it.
Mix Dry Ingredients: In a mixing bowl, whisk together the all-purpose flour, cocoa powder, sugar, baking powder, baking soda, and salt until well combined.
Combine Wet Ingredients: In a separate bowl, mix the eggs, milk, brewed coffee, vegetable oil, and vanilla extract. Stir until well incorporated.
Combine Mixtures: Gradually add the wet ingredients to the dry ingredient mixture. Stir until you have a smooth batter.
Bake: Pour the batter into the greased pan and bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.
Prepare the Mocha Mousse: While the cake is baking, whip the heavy cream in a mixing bowl until stiff peaks form. In another bowl, fold the melted chocolate, instant coffee granules, and powdered sugar into the whipped cream until fully combined.
Cool the Cake: Once the cake is baked, allow it to cool completely before spreading the mocha mousse over the top.
Serve and Enjoy: Slice up your masterpiece and serve with a sprinkle of cocoa or chocolate shavings as garnish, if desired.