Set oven to 350°F (175°C). For two 8-inch (20 cm) cake pans, cut a circle of baking parchment and place it in the bottom of each.

Using a hand whisk or food mixer, combine cocoa powder and boiling water and beat until lump-free. Incorporate the rest of the cake ingredients and mix just until the batter is uniform. Evenly distribute between the pans.

Drop each pan on the counter to eliminate air pockets. Bake for 25–30 minutes, until the sponge bounces back when pressed and a knife tip or cake tester inserted in the middle comes out with no crumbs. Refrain from opening the oven before 20 minutes or the cakes might collapse. Let cool on a wire rack; take out of pans once the metal is comfortable to touch.

To make buttercream, stir room-temperature butter, icing sugar, and cognac together with a wooden spoon until creamy.

For assembly, set the flattest sponge on a cake stand. Apply 1/4 of the buttercream, followed by an equal quantity of jam, keeping about 1 cm clear at the edges (jam will spread when the top sponge is placed).

Apply another 1/4 of the buttercream on top of the cake, maintaining a clean smooth surface and extending it over the edge for a neat finish.

Cover the cake sides with the remaining buttercream to provide a base for chocolate fingers. Arrange fingers around the perimeter, standing them upright.

Prepare chocolate writing icing as directed on the package. Create a clock face and set the time to a few minutes before twelve. Scatter edible gold stars over the clock face, if using, and serve.