Preheat oven to 350 degrees. Butter and flour two 9-inch round cake pans and line the bottom with parchment paper. Set aside.

In a stand mixer or large bowl with an electric mixer, beat together the butter and sugar until well combined. Add the drained ricotta and blend until light and fluffy, about 4-5 minutes. Mix in the eggs, one at a time, incorporating well. Then add in the limoncello, lemon zest, and vanilla.

In a separate bowl, whisk the flour, baking powder, baking soda, and salt. Mix the dry ingredients into the wet in two batches, until just combined.

Pour the batter into prepared pans and smooth as needed. Bake 30-35 minutes, or until the cake is set and a toothpick inserted in the center comes out clean. Let cool in pan for at least 10 minutes before turning out onto a wire rack to cool completely before frosting.

To make the frosting, in a large bowl, cream together the butter and cream cheese. Add the powdered sugar, limoncello, and zest. Mix until well combined.

Place one layer of the cooled cake on a pedestal or cake plate and spread on about a cup of frosting. Place the top layer of the cake and spread the remaining frosting all over the cake. Garnish with sliced lemons if desired.