Biscuit Base: Preheat the oven to 180°C (350°F). Beat eggs and sugar until light and fluffy. Add water and mix well. Sift in flour, baking powder, and cocoa powder. Fold gently until combined. Pour into a greased and floured cake pan. Bake for 25-30 minutes. Let cool.
Cream Filling: Whisk eggs, sugar, condensed milk, and starch in a saucepan. Gradually add milk, stirring constantly. Cook until thickened. Let cool. Beat butter until creamy. Gradually add milk mixture and vanilla, beating until smooth.

Assemble the Cake: Slice the biscuit base horizontally. Mix water and condensed milk for impregnation. Brush each layer with the mixture. Spread cream filling between the layers and on top.
Chocolate Glaze: Combine cocoa powder, sugar, sour cream, and butter in a saucepan. Heat until smooth and glossy. Pour over the cake.
Chill and Serve: Refrigerate for a few hours or overnight. Slice and serve chilled.
Prep Time: 40 minutes | Cooking Time: 30 minutes | Total Time: 70 minutes + chilling
Kcal: 560 kcal | Servings: 12