Banana Lemon Layer Cake

Ingredients

• The Cake
• 2 1/4 cups cake flour
• 1 1/4 teaspoons baking powder
• 1/2 teaspoon salt
• 1/2 cup butter, at room temperature
• 1 cup granulated sugar
• 1/2 cup light brown sugar, firmly packed
• 2 eggs
• 1/2 teaspoon grated lemon zest
• 1 cup mashed very ripe banana
• 1 teaspoon vanilla extract
• 1/4 cup milk
• 3/4 cup chopped walnuts
• The Frosting
• 1/2 cup butter, at room temperature (1 stick)
• 4 1/2 cups confectioners' sugar
• 3/4 teaspoon grated lemon zest
• 3 -5 tablespoons fresh lemon juice