Preheat oven to 350F. Butter two 8" cake pans and line the bottoms with parchment paper.

In a large bowl, combine the lemon zest and sugar. Mix with your fingers to help release the lemon essence. Remove half of the sugar to a smaller bowl.

Separate the eggs by adding the egg whites to the bowl of a stand mixer fitted with the whisk attachment. Add the yolks to the larger bowl of (half) lemon-sugar.

Whip the egg whites until soft peaks, then gradually add the remaining lemon-sugar in the smaller bowl. Beat until stiff peaks. Set aside.

In the egg yolks bowl, whisk vigorously for 1 minute, until pale and fluffy. Add the milk, vanilla, 2 tablespoons lemon juice, sour cream, and melted butter. Whisk very well.

Add the flour, baking powder, and salt to the egg yolks mixture. Beat for 1 minute, until smooth.

Using a spatula, gently fold the flour-egg yolks mixture into the whipped egg whites. Try to keep the egg whites fluffy and firm.

Once halfway incorporated, add the chopped raspberries. Fold just until incorporated.

Divide the batter between the prepared cake pans.

Bake for 20-25 minutes, until golden on top and a toothpick inserted into the centers comes out clean. The centers should also be firm to the touch and not jiggly.

Let cool in the pan for 15 minutes then transfer to a wire rack to cool completely.

Combine the limoncello and sugar in a saucepan over medium high heat. Stir until the sugar dissolves, about 5-6 minutes. Set aside to cool completely.

In the bowl of a stand mixer fitted with the whisk attachment, beat the softened butter until smooth.

Add two cups of the powdered sugar and beat until incorporated. Add the heavy cream and beat another 2 minutes.

Add another cup of powdered sugar and beat 2-3 minutes. If desired, add the remaining cup of powdered sugar and beat 4-5 minutes, until a light and fluffy buttercream. Even if not adding the last cup of powdered sugar, beat for 4-5 minutes at the end.

Add the vanilla bean paste and beat for 30 seconds.

Slice the completely cooled cakes in half lengthwise.

Add a little frosting to the bottom of the cake plate, then the first cake layer. Brush the cake layer with 1/4th of the limoncello syrup. Add 1/3-1/2 cup buttercream and spread out evenly. Add a thin layer of)about 3-4 tablespoons) of raspberry jam or lemon curd. Repeat with remaining cake layers. Frost the outside of the cake with the remaining buttercream. Decorate the top of the cake with fresh raspberries to serve!