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 well incorporated, then add the lemon zest and sour cream and beat until well combined.

Gradually add half of the sifted dry mixture followed by half of the liquid ingredients (buttermilk and lemon juice). Mix on low speed until all ingredients are combined, then add remaining dry and liquid ingredients and mix just until combined.

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

Divide the batter evenly between the three pans, about 1 ¾ cups per pan. Bake for 28-32 minutes. Allow to cool completely.

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

In the chilled bowl, beat the mascarpone and slowly pour in about ¼ cup of heavy cream, allowing it to liquefy. Then add the remaining cream and beat on high until soft peaks form.

Add powdered sugar and lemon extract, mixing on low until incorporated, then continue beating until stiff peaks form.

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

Pipe a layer of frosting and then spread half of the lemon curd over the frosting.

Add the second layer of cake and repeat with the remaining lemon curd. Add the final layer.

Fill gaps with frosting and create a crumb coat. Frost the top and sides of the cake and garnish with blackberries.