Preheat the oven to 350°F. Prepare three 8-inch round baking pans, line the bottom with parchment paper, grease the sides and dust with flour.

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. Add the lemon zest and sour cream, beating until well combined.

Gradually add half of the dry mixture to the batter, followed by half of the liquid ingredients. Mix on low speed until all ingredients are incorporated. Add the remaining dry and liquid ingredients and mix just until combined.

Toss the blackberries with 2 tablespoons of flour, then gently fold them into the batter.

Divide the batter evenly between the three pans. Bake at 350°F for 28-32 minutes. Test for doneness with a toothpick. Allow to cool completely.

Chill the mixing bowl and whisk attachment in the freezer for 5 to 10 minutes.

Beat the mascarpone cheese on medium-low speed while slowly adding about ¼ cup of heavy cream. Then add the remaining cream and increase to high speed until soft peaks form.

Add the powdered sugar and lemon extract, beating on low to incorporate, then high until stiff peaks form.

Level the top of the cake layers if needed. Place the bottom layer on a cake board and frost with a dollop of frosting.

Pipe a layer of frosting on the first layer and spread half of the lemon curd over it.

Add the second layer of cake and repeat the frosting and curd steps.

Add the final layer, using frosting to fill gaps and create a crumb coat. Frost the top and sides of the cake and garnish with blackberries.