Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, or line them with parchment paper.

In a large mixing bowl, beat the egg whites with a hand mixer or stand mixer until soft peaks form. In a separate bowl, whisk together the sugar, whole milk, melted butter, lemon zest, and vanilla extract.

In another bowl, sift together the self-rising flour, salt, and baking powder.

Gently fold the dry ingredients into the wet ingredients, alternating with the beaten egg whites. Start with a small amount of flour mixture, then add some of the egg whites, and continue alternating until everything is well combined. Be careful not to deflate the egg whites.

Pour the batter evenly into the prepared cake pans.

Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center of the cakes comes out clean. Let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

In a large bowl, beat the heavy whipping cream with a hand mixer until soft peaks form. In another bowl, combine the mascarpone cheese, powdered sugar, lemon zest, lemon juice, and vanilla extract. Mix until smooth.

Gently fold the whipped cream into the mascarpone mixture until fully combined, making sure not to deflate the whipped cream.

Once the cakes are completely cool, carefully slice each cake in half horizontally to create four layers. Place the first layer on a serving platter and spread a generous layer of lemon cream filling on top.

Add the second layer and repeat the process with more lemon cream filling. Continue until all the layers are stacked. Frost the top and sides of the cake with any remaining lemon cream filling.

Garnish with extra lemon zest or fresh berries if desired. Slice and serve immediately, or refrigerate for an hour to allow the flavors to meld together.