Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a large bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs, one at a time, mixing well after each addition. Then, add the lemon zest and lemon juice.
In a separate bowl, whisk the flour, baking powder, baking soda, and salt together.
Gradually add the dry mixture to the wet ingredients, alternating with buttermilk, starting and ending with the flour mixture.
Fold in the fresh blueberries gently to avoid breaking them.
Divide the batter evenly between the prepared pans and smooth the tops with a spatula.
Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.
As the cakes cool, prepare the mascarpone frosting by mixing mascarpone cheese and powdered sugar until smooth and creamy.
Once the cakes are completely cool, place one layer on a serving plate and spread a layer of lemon curd on top.
Add a layer of mascarpone frosting over the lemon curd, then place the second cake layer on top.
Frost the top and sides of the cake with the remaining mascarpone frosting, smoothing it evenly.
Finally, garnish the top with extra blueberries and a drizzle of lemon curd if desired.
