1. Prepare: Preheat oven to 350°F. Grease and flour two 9-inch round cake pans.
2. Dry Ingredients: In a medium bowl, whisk together cake flour, baking powder, baking soda, and salt.
3. Cream Butter and Sugar: In a large bowl, cream together softened butter and granulated sugar until light and fluffy.
4. Egg Whites: In a separate clean bowl, beat egg whites until stiff peaks form.
5. Combine Wet and Dry: Gradually add the dry ingredients to the butter mixture, alternating with the milk, beginning and ending with the dry ingredients. Mix until just combined.
6. Add Remaining Wet: Stir in vegetable oil, sour cream, vanilla extract, and lemon extract.
7. Fold in Egg Whites: Gently fold the beaten egg whites into the batter until just combined. Do not overmix.
8. Bake: Pour batter evenly into the prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
9. Cool: Let cakes cool in the pans for 10 minutes before inverting them onto a wire rack to cool completely.

Raspberry Filling

1. Combine: In a small saucepan, combine fresh raspberries, sugar, lemon juice, and water.
2. Simmer: Bring to a simmer over medium heat and cook until the raspberries have softened and the mixture has thickened slightly, about 10-15 minutes.
3. Cool: Let the filling cool completely.

Mascarpone Frosting

1. Cream Cheese and Butter: In a large bowl, cream together softened mascarpone cheese and butter until smooth and creamy.
2. Add Sugar: Gradually add sifted powdered sugar, mixing well after each addition.
3. Add Remaining Ingredients: Stir in milk, salt, and vanilla extract (or vanilla bean paste). Mix until smooth and well combined.

Assembly

1. Prepare Piping Bags: Put the mascarpone frosting in one piping bag and the raspberry filling in another.
2. Layer Cakes: Once the cakes are completely cooled, place one cake layer on a serving plate.
3. Pipe Fillings: Pipe swirls of mascarpone frosting and raspberry filling in the center of the cake layer.
4. Top with Second Layer: Place the second cake layer on top.
5. Frost Cake: Frost the entire cake with the remaining mascarpone frosting.
6. Decorate: Decorate the top of the cake as desired. Fresh raspberries and sprigs of mint can be added for decoration.
7. Chill: Refrigerate the cake for at least 30 minutes before serving.