Purple Velvet Cake

Ingredients

• 2⅛ cups all-purpose flour
• ¼ cup unsweetened cocoa powder
• 1 teaspoon baking soda
• 1 teaspoon baking powder
• ¼ teaspoon salt
• 8 tablespoons unsalted butter (softened)
• 1½ cups granulated sugar
• 2 eggs (at room temperature)
• 1 teaspoon vanilla extract
• 1 cup buttermilk
• 1 teaspoon white vinegar
• Food coloring (if desired)
• 8 ounces white chocolate
• 12 ounces cream cheese (softened)
• 6 ounces unsalted butter (softened)