Cake Preparation: Preheat oven to 350 F. Grease and flour three 9-inch round cake pans.
In a large bowl, cream together butter and sugar; set aside. In a separate bowl, combine flour, Clabber Girl Baking Powder and salt. Add coconut; combine with creamed mixture. Stir in milk and extracts and beat for two minutes with an electric mixer on medium speed.
In a medium bowl, combine egg whites and cream of tartar. Beat at high speed until stiff peaks form. Fold egg whites into batter.
Spread batter into 3 prepared cake pans. Bake at 350 F for 20 to 25 minutes.
Cool in pans on wire racks for 5 to 10 minutes before removing cake from pan. Let layers cool completely.
Lemon Curd Filling Preparation: In a small bowl, mix egg yolks until well combined and lemon-colored; set aside.
In a saucepan, combine cornstarch and sugar. Mix with wire whisk until combined. Stir in lemon zest and lemon juice; begin to cook, stirring constantly. Add margarine when mixture begins to heat up. Cook until mixture starts to bubble. Take about 1/2 cup of lemon mixture and slowly stir into eggs, a little at a time, until well combined. Pour mixture back into saucepan and bring to boil. Cook for 2 minutes, stirring constantly. Mixture should be thickened. Divide into 2 halves.
Marshmallow Frosting Preparation: In a medium bowl, mix butter and marshmallow cream with electric mixer until well combined. Add extract and milk; add powdered sugar, a little at a time, mixing after each addition.
*For a thicker frosting add more sugar; for a thinner frosting (or glaze) add more milk.
When layers have completely cooled, put 1/2 of lemon curd filling on top of first layer. Add next layer and the second 1/2 of lemon curd filling. Add top layer and frost top and sides with Marshmallow Frosting. Sprinkle top of frosted cake with 1/2 to 1 cup flaked coconut.