How to make it

1. Preheat your oven to 350°F (175°C). Grease and flour two 8-inch (20 cm) round cake pans.
2. In a large bowl, whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt.
3. Add the eggs, milk, oil, and vanilla extract. Mix until well combined.
4. Stir in the boiling water until the batter is smooth. It will be thin.
5. Divide the batter evenly between the prepared pans. Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
6. Let the cakes cool in the pans for 10 minutes, then turn them out onto a cooling rack to cool completely.
7. While the cakes cool, make the pudding filling: In a saucepan, whisk together the sugar, cocoa powder, cornstarch, and salt.
8. Gradually whisk in the milk until smooth. Cook over medium heat, stirring constantly, until the mixture thickens and begins to boil.
9. Remove from heat and stir in the vanilla extract and butter until smooth. Let cool slightly before using.
10. Once the cakes are cool, cut each layer in half horizontally to create four layers.
11. Reserve one layer and crumble it into fine crumbs.
12. Place one cake layer on a serving plate. Spread with a third of the pudding filling. Repeat with the remaining layers, ending with the pudding on top.
13. Press the reserved cake crumbs onto the sides and top of the cake.
14. Chill the assembled cake for at least 1 hour before serving.