Lemon Sponge Cake

Ingredients

• 1 1/4 cups flour
• 2 tablespoons cornstarch
• 1/2 teaspoon salt
• 7 large eggs at room temperature separated - 7 yolks in one bowl, 6 whites in another
• 1 1/2 cups sugar
• 2 teaspoons lemon zest, finely grated
• 2 teaspoons orange zest, finely grated
• 1/4 cup orange juice
• 1/4 cup lemon juice
• 1 1/2 teaspoons vanilla extract
• 1/2 teaspoon cream of tartar
• 3 cups confectioners sugar sifted
• 2 tablespoons butter, extrasoft
• 1 teaspoon lemon juice
• 1 teaspoon lemon zest, finely grated
• 1/2 cup orange juice