Preheat your oven to 350°F.
Grease and flour two 9-inch round cake pans.
In a large bowl, cream together butter and sugar until the mixture is light and fluffy.
Then, add the eggs one at a time, mixing well after each addition.
In a separate bowl, combine flour, baking powder, and salt.
Gradually add these dry ingredients to the wet mixture, alternating with whole milk, until well combined.
Fold in lemon zest and fresh lemon juice.
Pour the batter evenly into the prepared cake pans.
Bake for 25 to 30 minutes or until a toothpick inserted into the center of the cakes comes out clean.
Cool the cakes on a wire rack.
Whip the heavy cream until soft peaks form, then fold in the mascarpone cheese.
Once the cakes are completely cool, spread the cream mixture between the layers and on top.