Cake:2 cups (500 g) pastry cream2 cups (500 g) chocolate pastry cream7 oz (200 g) Maria cookies (or any plain tea biscuits)1 2/3 cups (400 ml) sweetened milkUnsweetened cocoa powder, to taste (for dusting)Pastry Cream:2 cups (500 ml) milk5 egg yolks1/2 cup (100 g) sugar1/2 cup + 1 tbsp (70 g) cornstarch (Maizena)1/4 cup (30 g) all-purpose flourZest of 1/2 lemonChocolate Pastry Cream:2 cups (500 ml) milk4 egg yolks4.2 oz (120 g) dark chocolate (bittersweet)1/2 cup (100 ml) heavy cream1/4 cup (35 g) cornstarch (Maizena)3 tbsp (25 g) all-purpose flour1 packet (about 1 tbsp) vanilla sugar1/2 cup (100 g) sugar