Melt 80 grams of butter in a saucepan over low heat, then combine with 100 ml of milk, 100 ml of water, and ½ teaspoon of salt, stirring until smoothly melted. In a separate bowl, whisk together 500 grams of flour and 1 teaspoon of baking powder, then gradually add this mixture to the heated liquids, stirring continuously until the dough forms a smooth ball. Allow the dough to cool slightly, then incorporate 4 eggs one at a time, mixing until the dough is smooth and sticky.

Preheat your oven to 400°F (200°C) and prepare a 25cm round baking pan by lining it with parchment paper. Divide the prepared dough into two equal portions and flatten each piece directly into the pan. Bake both layers in the preheated oven for 20 minutes, or until they are lightly golden and firm to the touch. Once baked, remove them from the oven and allow the layers to cool completely before assembling.

To create the luscious filling for the Melt-in-Your-Mouth Cake, beat 2 eggs with 150 grams of sugar in a bowl until the mixture is pale and fluffy. Gradually add in 50 grams of flour and 100 ml of milk, whisking until a smooth batter forms. Transfer this mixture to a saucepan and cook over medium heat, stirring continuously until it thickens and begins to boil, approximately 3 minutes. Remove from heat and let it cool, then blend in 180 grams of softened butter until the filling is velvety and smooth.

Begin layering your Melt-in-Your-Mouth Cake by placing the first baked layer on a serving platter. Spread half of the creamy filling evenly on top, then gently place the second layer over it. Finish by spreading the remaining cream filling on top of the second layer, smoothing it out for an appealing presentation. To achieve the perfect consistency, refrigerate the assembled cake for at least 2 hours, allowing the flavors to meld beautifully.