Start by preheating your oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper so the cakes come out easily after baking.

In a medium bowl, whisk together the flour, baking powder, and salt. Set it aside. In a larger bowl, beat together the butter and sugar with an electric mixer until it’s light and fluffy (about 3-5 minutes). Add the eggs one at a time, beating well after each, and then stir in the vanilla extract.

Gradually add the dry ingredients to the wet mixture, alternating with the milk. Start and finish with the flour mixture, and mix just until combined. Don’t overdo it—keep it light.

Evenly divide the batter between the two prepared pans and smooth the tops with a spatula. Pop them in the oven and bake for 30-35 minutes, or until a toothpick comes out clean when inserted in the center. Let the cakes cool in the pans for about 10 minutes, then flip them onto a wire rack to cool completely.

In a small bowl, dissolve the gelatin in water and let it sit for 5 minutes to bloom. Meanwhile, heat the milk and sugar in a saucepan over medium heat until it’s warm but not boiling. In another bowl, whisk the egg yolks until smooth. Gradually pour the warm milk into the egg yolks, whisking constantly to prevent curdling.

Return the egg yolk mixture to the saucepan and cook over low heat, stirring constantly, until it thickens enough to coat the back of a spoon (about 5-7 minutes). Remove from heat, and stir in the bloomed gelatin until it dissolves completely. Let this custard mixture cool to room temperature.

While the custard cools, whip the heavy cream, powdered sugar, and vanilla extract with an electric mixer until stiff peaks form. Once the custard has cooled, gently fold it into the whipped cream using a rubber spatula. Be gentle so the mousse stays light and airy.

Once the cakes are completely cool, place one layer on a serving plate. Spread half of the mousse filling on top. Place the second cake layer on top, then cover it with the remaining mousse. If you want, you can garnish with whipped cream or fresh berries for extra flair.