Sweet Potato Cake with White Chocolate Cream Cheese Frosting

1 ½ cups butter, softened
2 cups sugar
1 teaspoon vanilla extract
6 large eggs, separated
2 1/4 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon ground ginger
1 teaspoon ground cinnamon
½ teaspoon salt
½ teaspoon ground nutmeg
1 cup buttermilk
2 cups finely grated sweet potato
1 cup chopped walnuts

Preheat oven to 350 degrees. Spray 3 (8in) cake pans with nonstick baking spray with flour. In a large bowl, beat butter, sugar, and vanilla at medium speed with a mixer until fluffy.  Add egg yolks, beating until combined. In a medium bowl, combine flour, baking soda, ginger, cinnamon, salt and nutmeg. Gradually add to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating just until combined after each addition. In a medium bowl, beat egg whites at high speed with a mixture until stiff peaks form. Gently fold into batter. Gently stir in sweet potatoes and walnuts. Spoon batter into prepared pans. Bake for 20 to 23 minutes or until a wooden pick inserted comes out clean. Cool in pans for 10 minutes. Remove from pans, cool completely on wire racks. Spread White Chocolate-Cream Cheese Frosting evenly between layers and on top and sides of cake.

White Chocolate-Cream Cheese Frosting

1 (4oz) white chocolate baking bar, chopped
1/3 cup heavy whipping cream
1 cup butter, softened
16 oz. cream cheese softened
2lbs. powdered sugar

In a small sauce pan, combine chopped white chocolate and cream. Cook over medium-low heat, stirring constantly, until chocolate melts and mixture is smooth.  Remove from heat, and cool for 1 hour. In a large bowl, beat butter and cream cheese at medium speed with a mixer until creamy. Add white chocolate mixture, beating until combined. Gradually add powdered sugar, beating until smooth. Note: Cake layers can be made up to 1 month ahead; wrap cooled layers tightly in plastic wrap and Freeze. To serve, spread frosting on frozen cake layers (frozen layers are easier to frost), and thaw. Store thawed cake, covered, in refrigerator up to 3 days.