Cake 1 (6-ounce) package white chocolate baking bars, broken into small pieces 2 tablespoons milk 2 cups all-purpose flour 3/4 teaspoon baking soda 1/2 teaspoon salt 1/4 teaspoon baking powder 1/2 cup (1 stick) butter, softened 3/4 cup sugar 1 teaspoon vanilla extract 4 eggs 1 cup sour cream
Frosting 1 cup butter, softened 2 cups confectioners' sugar 6 ounces white chocolate or 6 ounces white baking bar, melted and cooled 3-5 tablespoons whipping cream or 3-5 tablespoons half-and-half
Preheat oven to 350 degrees F. Lightly grease two (8-inch) round baking pans with cooking spray, then line bottoms with waxed paper.
In a medium saucepan, combine white chocolate and milk over low heat, stirring constantly until chocolate is melted and mixture is smooth. Set aside.
Combine flour, baking soda, salt, and baking powder in a medium bowl and set aside. In a large bowl, beat butter and sugar until light and fluffy. Blend in melted baking bars and vanilla extract. Add eggs one at a time, beating well after each addition. Add flour mixture alternately with sour cream. Pour into prepared pans.
Bake 30 to 35 minutes or until a tester inserted in center comes out clean. Cool 10 to 15 minutes, then remove from pans and peel off waxed paper. Place in a wire rack to cool completely.
To make the white chocolate butter cream frosting, combine the butter and confectioners sugar in a large bowl and beat at low speed until fluffy. Add in melted white chocolate and whipping cream, 3 tablespoons at a time and add in more to achieve desired consistency. Beat on high speed for 3-4 minutes, scraping the bowl with a spatula. Spread frosting on top and sides of the cooled White Velvet Cake.