Salted caramel cake

Name: Salted caramel cake
Ingredients: Brown sugar buttermilk cake; 1/2 cup unsalted butter, room temperature; 1 cup 1 cup sugar; 3/4 cup packed brown sugar; 3 large eggs; 1 teaspoon vanilla; 2 1/4 cups cake flour, sifted; 1 cup buttermilk; 1 teaspoon baking soda; 1 teaspoon white vinegar; Caramel Sauce and Cream Cheese Frosting; 2 cups sugar; 12 tablespoons unsalted butter, cubed & room temperature; 1 cup heavy cream, room temperature; 1 tablespoon fleur de sel; 1/2 cup packed brown sugar; 5 ounces unsalted butter, room temperature, divided; 1/3 cup heavy cream; 8 ounces cream cheese, softened; 1/4 teaspoon salt; 2 cups powdered sugar