Preheat oven to 180°C (350°F). Grease and line two 8-inch round pans.
Beat eggs and sugar until light and fluffy (about 3 minutes).
Add oil and milk, mixing until combined.
Sift in flour and cocoa powder, folding gently.
Fold in baking powder. Divide batter evenly between pans.
Bake for 30-35 minutes or until a toothpick comes out clean. Cool completely.
Dissolve cornstarch in 3 tbsp of milk.
In a saucepan, combine all vanilla cream ingredients. Cook over medium heat, stirring constantly, until thick (about 10 minutes). Cover with plastic wrap touching the surface to prevent a skin. Cool completely.
Combine brigadeiro ingredients in a saucepan. Cook over low heat, stirring constantly, until thickened (about 15 minutes). Cool before use.
Heat cream until steaming (do not boil). Pour over chopped chocolate. Let sit for 2 minutes, then stir until smooth. Cool slightly.
Place one cake layer on a serving plate. Spread brigadeiro evenly.
Arrange a single layer of chocolate biscuits over the brigadeiro.
Spread cooled vanilla cream over biscuits.
Place the second cake layer on top.
Press biscuit crumbs gently around the sides and top.
Pour melted chocolate in a zigzag pattern for decoration.