Prepare the Oven and Pans:

• Preheat your oven to 350°F.
• Grease and flour three 8-inch round baking pans. Line the bottoms with parchment paper for easy removal.
• If you have bake-even strips, soak them in water and wrap them around the pans. This will help the cakes bake more evenly.

Make the Cake Batter:

• In a large mixing bowl, combine the sugar, vegetable oil, eggs, and lemon extract.
• Beat on medium speed for about 2 minutes, until the mixture is light and fluffy.
• Zest the lemons directly into the batter and then juice them to get ¼ cup of fresh lemon juice.
• Add the lemon zest, lemon juice, and sour cream to the batter and beat until well combined.
• In a separate bowl, whisk together the flour, baking powder, and salt.
• Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, and mix until just combined. Be careful not to overmix.  
• Toss the blueberries with 2 tablespoons of flour to prevent them from sinking to the bottom of the cake.
• Gently fold the blueberries into the batter, reserving a small handful to sprinkle on top.

Bake the Cakes:

• Divide the batter evenly among the prepared pans.
• Sprinkle the remaining blueberries on top of the batter in each pan.
• Bake for 20-23 minutes, or until a toothpick inserted into the center comes out clean.
• Rotate the pans halfway through baking to ensure even cooking.
• Once baked, remove the cakes from the oven and let them cool completely in the pans before frosting.

Make the Lemon Mascarpone Frosting:

• In a large mixing bowl, beat the heavy whipping cream with an electric mixer until stiff peaks form.
• Gradually add the powdered sugar and vanilla extract, beating until smooth and fluffy.
• In a separate bowl, beat the cold mascarpone cheese until smooth and creamy.
• Gently fold the whipped cream into the mascarpone cheese until combined.
• Fold in the lemon curd until evenly distributed.

Assemble the Cake:

• Once the cakes are completely cool, level the tops with a serrated knife if needed.
• Place one cake layer on a serving plate and top with a layer of frosting.
• Repeat with the remaining cake layers and frosting.
• Frost the entire cake with the remaining frosting.
• Decorate as desired with fresh blueberries, lemon zest, or lemon slices.