Good-Cooking - Lemony White Cake with Milk Chocolate Ganache

Ingredients

• 2 1/4 cups cake flour
• 3 teaspoons baking powder
• 1/2 teaspoon salt
• 1/2 cup (1 stick) unsalted butter, softened
• 1 1/2 cups granulated sugar
• 2 teaspoons finely grated lemon zest
• 1/2 teaspoon lemon extract
• 1/2 cup egg whites (from about 4 large eggs)
• 1 1/4 cups milk
• Zest of 2 lemons removed in long strips with a vegetable peeler
• 2 cups heavy whipping cream
• 4 tablespoons (1/2 stick) unsalted butter, softened
• 20 ounces milk chocolate, cut into 1/4-inch pieces
• 4 ounces bittersweet chocolate, cut into 1/4-inch pieces