1/2 cup butter, softened
1/2 (8-oz.) package cream cheese, softened
1 1/4 cups sugar
3/4 cup firmly packed dark brown sugar
4 large eggs
1 teaspoon vanilla extract
3 cups all-purpose flour
1 teaspoon baking powder
1/2 teaspoon baking soda
1/2 teaspoon salt
1 (8-oz.) container sour cream
8 ounces chopped semisweet chocolate
1/4 cup whipping cream
2 tablespoons whipping cream
Salted Caramel Buttercream
Garnishes: sea salt flakes and caramels, cut into quarters