1. Preheat oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.

2. In a medium bowl, whisk together flour, baking powder, and salt.

3. In a large bowl, cream together butter and granulated sugar until light and fluffy.

4. Add eggs one at a time, beating well after each addition. Stir in vanilla extract, lemon juice, and lemon zest.

5. Alternately add the dry ingredients and milk to the wet mixture, beginning and ending with the dry ingredients.

6. Gently fold in the blueberries.

7. Divide batter evenly between prepared cake pans and smooth the tops.

8. Bake for 25–30 minutes, or until a toothpick inserted into the center comes out clean.

9. Cool cakes in the pans for 10 minutes, then turn out onto wire racks to cool completely.

10. To make the mascarpone frosting, combine mascarpone cheese, powdered sugar, and vanilla extract in a bowl and beat until smooth.

11. Spread the mascarpone frosting between the cake layers and over the top and sides of the cake.

12. Garnish with extra blueberries and lemon zest, if desired.