8 ounces graham cracker crumbs 6 tablespoons melted butter divided 1 (12 ounce) container of ricotta cheese 2 (8 ounce) packages cream cheese at room temperature 1 cup sugar 1/2 cup limoncello liqueur 4 large eggs at room temperature 1 teaspoon fiori di sicilia extract or 1 teaspoon vanilla extract lemon curd topp