Crush the biscotti and mix with the melted butter, cocoa powder, and 250 ml of milk until combined. Press this mixture into a baking pan to form a crust.

In a saucepan, heat the remaining milk along with flour, cornstarch, and sugar over medium heat, stirring continuously until a pudding-like consistency is achieved.

Remove from heat and add the butter and vanilla extract, stirring until well incorporated.

For a velvety texture, consider blending the mixture before pouring it over the prepared crust.

Pour the creamy filling over the crust and refrigerate for one hour to set.

Melt the chocolate chips with 4 tablespoons of milk until smooth. Drizzle it over the chilled dessert and return to the fridge for another hour.

Slice the squares into bite-sized pieces and serve topped with chopped nuts.