Make the lemon curd

1. Prepare the lemon curd following my easy recipe. Let it cool completely before using.

Prepare the lemon sponge cakes

1. Preheat your oven to 165°C (330°F). Line three 6-inch cake pans with parchment paper and lightly grease the sides.
2. In the large mixing bowl of a stand mixer, beat the eggs, sugar, and lemon zest together for several minutes until the mixture is pale and has doubled in volume. Meanwhile, whip the heavy cream into soft peaks with a hand mixer.
3. Gently fold the dry ingredients (cake flour, baking powder, salt) into the egg mixture. Finish by folding in the whipped cream with a rubber spatula.
4. Divide the batter evenly between the pans and bake for about 40 minutes, or until a toothpick comes out clean. Let the cakes cool slightly, then carefully remove them from the pans and cool completely. (Optional: trim the top crust with a knife to get perfectly white and even sponge layers.)

Make the mascarpone frosting

1. Whip the cold mascarpone cheese, heavy cream, powdered sugar, and vanilla extract together with a hand mixer until smooth and fluffy.

Make the lemon buttercream

1. Prepare the lemon buttercream following my simple recipe.

Assemble the cake

1. Place the first cake layer on a cake board set on a turntable. Pipe a ring of lemon buttercream around the edge, fill the center with mascarpone frosting, and add a layer of lemon curd. Repeat with the remaining layers.
2. Cover the entire cake with lemon buttercream, smooth it out with an icing smoother, and decorate as you like. Chill the cake until ready to serve, and let it sit at room temperature for about 30 minutes before slicing.