Perfect Chocolate Cake

1 . Stage

Start cake: Place cocoa in a medium bowl. Gently pour boiling water over top and stir to combine; let cool, about 15 minutes.

2 . Stage

Meanwhile, preheat the oven to 350 degrees F (175 degrees C). Grease and flour three 9-inch round cake pans.

3 . Stage

Sift together flour, baking soda, salt, and baking powder into a mixing bowl.

4 . Stage

Combine sugar and butter in a large mixing bowl; beat with an electric mixer until creamy. Add eggs, one at a time, mixing well after each addition. Stir in vanilla. Add flour mixture alternately with the cooled cocoa mixture, mixing only until combined. Pour 1/3 of the cake batter into each of the prepared pans, spreading evenly.

5 . Stage

Bake in the preheated oven until a toothpick inserted into the centers comes out clean and cakes pull away from the sides of the pans, 18 to 22 minutes. Remove cakes from the oven and set on a wire rack to cool for about 5 minutes. Run a table knife around the edges to loosen. Invert cakes carefully onto the wire rack and let cool completely, about 20 more minutes.

6 . Stage

While the cakes are cooling, make frosting and filling: Beat butter for frosting in a mixing bowl until creamy. Gradually mix in confectioners' sugar, cocoa, and vanilla; continue to mix until light and fluffy, 7 to 10 minutes. Set aside.

7 . Stage

Make filling: Whip heavy cream and vanilla in a bowl until cream becomes thick. Add confectioners' sugar and continue to whip until stiff but not too grainy.

8 . Stage

Fill and frost cake: Remove cooled cake layers from pans. Trim any top surfaces to make them flat. Place one layer on a nice plate and spread 1/3 of the filling over the top. Top with another layer and another 1/2 of the remaining filling. Place the remaining cake layer on top. Spread frosting around the sides of the layers, leaving a ridge that extends up over the top edge. Spread the remaining filling over the top of the cake, inside the ridge of frosting.