Prepare Batter: In a bowl, whisk eggs and sugar until fluffy. Add milk, oil, vanilla, baking powder, cocoa powder, and flour. Mix with a hand mixer until smooth.

Bake Sponge: Pour the batter into a greased baking dish. Bake in a preheated oven at 170°C (340°F) for 30 minutes. Remove and let cool completely.

Hollow Out: Using a fork, gently scrape off the top layer of the cake to create a shallow "trench." Leave the bottom and sides intact. Set the removed cake pieces aside.

Add Fruit: Slice the bananas and arrange them in an even layer inside the hollowed-out section of the cake.

Whip Cream: Combine the whipped cream mix, pastry cream mix, and 3 cups of cold milk in a bowl. Beat until very stiff peaks form.

Assemble: Spread the cream mixture evenly over the bananas, creating a slight dome shape.

Create "Soil": Place the reserved cake pieces in a food processor and pulse into fine crumbs. Sprinkle the crumbs over the cream until it is completely covered.

Chill & Serve: Refrigerate for at least 1 hour to set. Slice into squares and enjoy chilled.