Mix Ingredients: In a saucepan, whisk together the egg, caster sugar, vanilla sugar, cornstarch, and milk until well combined.

Cook Cream: Place the saucepan over medium-high heat and stir continuously until the cream thickens. Transfer to a glass container, cover with plastic wrap, and let cool completely.

Beat Eggs: In a deep bowl, beat the eggs, sugar, and salt with a mixer on high speed until foamy and pale, about 3-4 minutes.

Add Liquids: Gradually mix in the milk and vegetable oil, pouring them in a thin stream while continuing to beat.

Incorporate Dry Ingredients: Sift the flour and baking powder into the bowl. Add the ground almonds and mix with a silicone spatula until the dough is smooth and lump-free.

Prepare Baking Dish: Line a rectangular baking dish with parchment paper and pour the dough in, spreading it evenly. Sprinkle almond flakes on top.

Add Cream: Transfer the cooled cream into a pastry bag and pipe a mesh of cream over the dough by pressing down with your hand.

Bake: Bake in a preheated oven at 170°C (340°F) for about 40 minutes, or until golden brown and cooked through.

Cool and Serve: Remove the cake from the oven and transfer it to a plate.

Finish with Powdered Sugar: Dust with powdered sugar before serving.

Enjoy: Cut into portions and enjoy this delectable cake!