Preheat oven to 350 degrees. Lightly grease two 9-inch round cake pans. Line pans with parchment paper; grease and flour parchment.
CAKE: In a medium bowl, whisk together flour, baking soda, and salt; set aside.
In a large bowl, using an electric hand mixer, cream together butter and sugar. Add eggs one at a time, beating well after each addition.
Combine buttermilk, limoncello, lemon zest and lemon juice. Add alternately with flour, beating well after each addition.
Pour batter into prepared cake pans. Bake cakes for 20 to 25 minutes. Cool completely in pans. Once cool, remove cakes from pans.
Place one layer on serving plate. Frost top with 1/3 frosting. Place second layer on top. Frost with one half of frosting. Use remaining frosting to frost sides of cake. Decorate top with white chocolate shavings if desired.
FROSTING: In a large bowl, cream together mascarpone cheese and lemon curd; set aside.
In a separate bowl, whip cream, slowly adding confectioners’ sugar until light and fluffy. Gently fold in mascarpone cheese/lemon curd mixture into whipped cream until completely combined. Frost as directed above.