With the rack in the middle position, preheat the oven to 180 °C (350 °F). Line three straight edge 20-cm (8-inch) square pans with strips of parchment paper, letting it hang over each side. Butter the other two sides.
In a bowl, combine the flour, baking powder, and salt. Set aside.
In another bowl, cream the butter, sugar, and vanilla with an electric mixer for about 3 minutes. Add the eggs, one at a time, and beat until smooth. Add the oil. At low speed, add the dry ingredients alternately with the milk.
Spoon the batter into the pans. Bake for about 30 minutes or until a toothpick inserted in the centre of the cake comes out clean.
Let cool. Unmould and let completely cool on a wire rack.
In the upper part of a double boiler, combine the sugar and egg whites. Heat gently, stirring constantly with a whisk. When the sugar is completely dissolved and the mixture is warm, remove from the double boiler.
Beat the egg white mixture with an electric mixer until it has cooled and stiff peaks form, about 15 minutes.
In another bowl, cream the butter with an electric mixer for about 2 minutes. Add half of the cooled meringue and beat until smooth. Add the remaining meringue and fold in well with a whisk.
In a small bowl, combine the boiling water and coffee. Set aside.
Evenly divide the buttercream into three bowls (about 625 ml / 2 ½ cups each). In the first bowl, with a whisk, stir in the vanilla. In the second bowl, add the melted chocolate. In the third bowl, whisk in the coffee. Set aside.
Cut the cakes in half horizontally. Spread the dulce de leche inside the first cake, the chestnut cream inside the second and 125 ml (½ cup) of chocolate buttercream in the third. Even out the edges of each cakes. Cut each cake into 16 squares.
Line a large or three small baking sheets with parchment paper, depending on the space you have in your refrigerator.
Place the coconut on a large plate, the grated chocolate in a second plate and the almonds in a third. Set aside.
Coffee Moka Cakes
With a pastry bag fitted with a small star tip of your choice, ice the sides and top of each chestnut cream-filled cake with a thin layer of coffee buttercream. Sprinkle with sliced almonds and place on baking sheet.
Chocolate Moka Cakes
Spread each chocolate-filled cake with a thin layer of chocolate buttercream. Press the frosted sides in grated chocolate and place the cakes on the baking sheet. With a pastry bag fitted with a small decorative tip of your choice, frost the top of each with moka cake with chocolate buttercream.
Caramel and Coconut Moka Cakes
Spread each caramel-filled cake with a thin layer of vanilla buttercream. Press the frosted sides in the coconut and place on the baking sheet. With a pastry bag fitted with a small decorative tip of yout choice, frost the top of each cake with vanilla buttercream. If desired, cover entirely with coconut.
Refrigerate the cakes for about 2 hours or until the buttercream is firm. This step will allow you to place them in an airtight container without damaging them. They will keep for 2 to 3 days in the refrigerator or 3 months in the freezer. Thaw in the refrigerator and bring to room temperature for at least 1 hour before serving.
For a pretty presentation, the cakes can be placed on flattened-out muffin paper liners.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.