Prepare the Cake:

Preheat Oven: Preheat the oven to 350°F (175°C). Grease and line two 8-inch round cake pans.

Dry Ingredients: In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.

Wet Ingredients: In a large bowl, beat the butter, granulated sugar, and brown sugar together until light and fluffy. Mix in the eggs one at a time, followed by the lemon zest, lemon juice, and vanilla extract.

Combine: Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. Mix until just combined.

Prepare Blueberries: Toss the blueberries with 1 tablespoon of flour to prevent them from sinking. Gently fold them into the batter.

Bake: Divide the batter evenly between the prepared cake pans. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.

Cool: Allow the cakes to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

Prepare the Mascarpone Frosting:

Whip: In a large bowl, beat the softened mascarpone cheese until smooth.

Add Cream: Gradually pour in the heavy cream and powdered sugar, whipping until soft peaks form. Stir in the vanilla extract and lemon zest if desired.

Assemble the Cake:

Frost: Place one cooled cake layer on a serving plate. Spread a layer of mascarpone frosting over the top. Place the second cake layer on top and frost the entire cake.

Serve: Garnish with fresh blueberries or lemon slices if desired. Slice and serve chilled.