In a double boiler over simmering water, combine fresh lemon juice, lemon zest, sugar, egg yolks, and salted butter. Stir constantly for about 10-15 minutes until the mixture thickens and coats the back of a spoon. Remove from heat and let it cool to room temperature before refrigerating for at least 1 hour to set.

Preheat your oven to 350°F (175°C) and grease three 8-inch round cake pans. In a mixing bowl, whisk together the all-purpose flour, baking powder, and baking soda. In a separate bowl, cream unsalted butter and sugar until light and fluffy, then add the egg yolks and vanilla extract. Gradually mix in the dry ingredients with the milk and lemon juice until just combined, avoiding overmixing.

Divide the cake batter evenly among the prepared pans, smoothing the tops with a spatula. Bake in the preheated oven for 22-25 minutes, or until a toothpick inserted in the center comes out clean. Once done, remove the pans from the oven and let them cool for 10 minutes before transferring the cakes to a wire rack to cool completely.

Once the cake layers are entirely cool, use a serrated knife to trim the tops if they have domed. Place the first layer on a serving plate and spread a generous amount of chilled lemon curd followed by mascarpone frosting. Add the second layer on top and repeat the process. For the top layer, spread mascarpone frosting evenly and feel free to get creative with decorations.

After assembling your Italian Lemon Mascarpone Layer Cake, cover it loosely with plastic wrap and refrigerate for at least 2 hours to allow the flavors to meld and the frosting to set. When ready to serve, slice with a sharp knife and enjoy the refreshing, creamy delight of this beautiful cake!