Preheat the oven to 350°F. Grease with butter then line a 13 by 9-inch cake pan with parchment paper.

Make the cake: In a mixing bowl, combine the flour, sugar, and salt.

In a saucepan over medium heat, melt the butter, then stir in the cocoa to combine. Add the boiling water, let the mixture boil for 30 seconds, then turn off the heat. Carefully pour the hot mixture over the dry ingredients and stir lightly.

Pour the milk into a small bowl. Whisk in the lemon juice (the milk will curdle). Add the eggs, baking soda, and vanilla (it will foam). Stir the milk mixture into the chocolate batter until fully incorporated.

Pour the batter into the prepared pan, spread evenly, and bake for 20 to 25 minutes or until a toothpick inserted into the center comes out clean. Let cool in the pan, then take a 2-inch biscuit cutter and cut out 24 rounds, cutting as close together as possible to avoid waste. (If you can stop yourself from eating it, save the cake that you can’t use for a chocolate parfait—just fill a cup with layers of the cake, chocolate pudding, halved cherries, and whipped cream.)

Have the ganache ready. Whip the cream with the powdered sugar until it holds very stiff peaks.

Lay 12 of the cake rounds on a clean surface. Slick each top with a thin layer of ganache and top each with 4 cherry halves. Cover the cherries with a tablespoonful of whipped cream, then top with a second cake round and gently press down so the whipped cream reaches the edges. Carefully transfer the assembled cakes to a wire rack set over a pan.

Run a knife around each cake to trim any protruding whipped cream. Pour the chocolate ganache over the cakes and distribute the ganache along the sides with a knife. Top with a stem-on cherry, transfer to a dessert plate, and serve.