Tweed Squares

Ingredients

• Cake:
• 2 egg whites
• 1/2 cup unsalted butter
• 2/3 cup white sugar
• 1 1/3 cups all-purpose flour
• 2 teaspoons baking powder
• 1 teaspoon salt
• 1/2 cup whole milk
• 1 teaspoon vanilla extract
• 1/2 cup miniature semisweet chocolate chips
• Frosting:
• 1/3 cup butter, softened
• 1 1/2 cups confectioners' sugar
• 2 egg yolks
• 1 teaspoon vanilla extract
• 1 pinch salt
• Topping:
• 3 (1 ounce) squares semisweet chocolate
• 2 tablespoons butter