For the Cake:

1. Preheat the oven to 350°F. Prepare three 8-inch round baking pans, line the bottom with parchment paper and grease the sides. Prepare your bake even stripes if desired.
2. In a large mixing bowl, combine the sugar, vegetable oil, eggs, and lemon extract. Beat on medium speed until the eggs and oil are well incorporated and the batter is lighter in color, about 2 minutes. Scrape down the bowl as needed.
3. Next, zest 2 lemons into the batter and then juice the lemons to get 1/4 cup of lemon juice. Add the lemon zest, lemon juice, and sour cream to the batter and beat until well combined.
4. Combine the dry ingredients in a separate bowl then add half the dry ingredients to the batter, beat on low speed while pouring in half of the buttermilk, and mix just until the flour starts to incorporate.
5. Finally, add the remaining dry ingredients and remaining buttermilk and beating until all of the ingredients are well combined.
6. Use a spatula to scrape down the sides of the bowl and stir the batter from the bottom to the top to ensure it’s well mixed.
7. Toss the blueberries with 2 tablespoons of flour. Then gently fold the blueberries into the batter, saving a small handful to drop on top of the cake batter.
8. Divide the batter evenly between the three pans, about 1 2/3 cups of batter per pan. Drop the remaining blueberries on top. Bake at 350°F for 20-23 minutes. Rotate your pans in the oven halfway through baking.
9. Test the cake for doneness by inserting a toothpick into the center of the cake. If the toothpick comes out clean, you cake is done. Remove from the oven and allow to cool completely.

For the Frosting:

1. Place the mixing bowl and whisk attachment in the freezer for 5 to 10 minutes to chill.
2. Spoon the cold mascarpone whipped cream into your bowl and beat on a medium-low speed (speed 3 on your stand mixer). Slowly pour in the heavy cream, allowing the mascarpone cheese to turn to a liquid consistency.
3. Then increase the mixing speed to high (speed 8-10) and beat it until soft peaks form.
4. Next, add the powdered sugar and vanilla extract, beating on low until sugar is incorporated. Then continue beating at high speed until stiff peaks form.

Assembly

1. Use a cake leveler to cut the domes off the top of the cake. Place a dollop of frosting on your cake board and place the bottom layer of cake on top of that.
2. Place half of the whipped cream in a large piping bag fitted with a large open round tip, or simply cut off the end of the piping bag. Pipe a layer of frosting and spread evenly. Then spread half of the lemon curd over the mascarpone filling.
3. Add the second layer of cake and repeat the above steps using all of the remaining lemon curd. Next, add the final layer of cake on top.
4. Use your piping bag to fill in any gaps between your layers and to create a crumb coat. Using an offset spatula or icing smoother, wipe away the excess frosting, leaving you just enough to coat the outside of the cake. Do not mix your crumb coating frosting back into your icing if it has cake debris in it.
5. Proceed to frost the top and sides of the cake using your offset spatula. Once the sides of the cake are covered, use an icing smoother to remove any excess frosting. You can take the end of your offset spatula and gently place them against the sides of the cake as your rotate your cake to add a little texture.
6. Use remaining frosting to pipe the florets on the top of the cake using an Ateco 809 tip (large open round). Garnish with lemon slices and leftover blueberries. This cake must be refrigerated.