Preheat the Oven:
Preheat your oven to 350°F (175°C). Grease and flour a 9-inch (23cm) round cake pan to ensure the cake comes out easily once baked.
Prepare Dry Ingredients:
In a medium bowl, sift together the flour, baking powder, and salt. This will help to evenly distribute the dry ingredients and prevent clumps.
Cream Butter and Sugar:
In a large bowl, beat the softened butter and granulated sugar together until light, fluffy, and pale in color. This usually takes about 4-5 minutes with an electric mixer. The fluffiness of the mixture is important for a light and airy cake.
Add Eggs and Vanilla:
Add the eggs one at a time, beating well after each addition. This ensures the eggs are fully incorporated and prevents the batter from curdling. After the eggs are incorporated, mix in the vanilla extract.
Alternate Adding Wet and Dry Ingredients:
Gradually add the dry flour mixture alternating with the milk, beginning and ending with the flour mixture. Mix on low speed just until combined. Be careful not to overmix, as this can lead to a dense cake.
Make the Chocolate Batter:
In a small bowl, mix the cocoa powder with hot water until smooth. Take about ⅓ of the cake batter and gently fold in the cocoa mixture to create the chocolate batter.
Marble the Cake Batter:
In the prepared cake pan, alternate spoonfuls of the vanilla and chocolate batters. Once both batters are in the pan, use a knife or skewer to gently swirl the two together, creating a marbled effect. Be sure not to over-swirl, as you still want distinct swirls in the finished cake.
Bake the Cake:
Bake for 45-50 minutes, or until a toothpick inserted into the center of the cake comes out clean. The baking time may vary slightly depending on your oven, so check after 45 minutes.
Cool the Cake:
Let the cake cool completely in the pan on a wire rack. This step is crucial to ensure the cake firms up and doesn’t break when you remove it from the pan.
Make the Chocolate Drizzle:
To make the chocolate drizzle, heat the heavy cream in a small saucepan over medium heat until it begins to simmer. Remove from heat and pour the cream over the chopped dark chocolate. Let it sit for 2 minutes, then stir until smooth and glossy.
Drizzle and Serve:
Once the cake has cooled, drizzle the chocolate sauce over the top before serving. Let the glaze set for a few minutes before slicing to ensure it holds its glossy finish.
