Pre-heat oven to 325 degrees.

In a medium sized bowl, sift together the flour, cream of tartar, and baking powder.

In a large bowl, combine room temperature egg whites and salt. Beat at high speed until soft peaks form. Fold 1/4 egg white mixture into the flour mixture until just incorporated. Continue adding the egg white mixture to the flour mixture in fourths until all is incorporated.

Grease and flour 4 9-inch round cake-pans. Bake at 325 degrees for 25 minutes or until a wooden toothpick comes out clean. Cool in pans for at least 10 minutes then remove to a cooling rack. When the layers are cool, cut the layers horizontally to make 8 layers.

On a cake stand, add a cake layer and spread lemon filling over the top and continue to add the cake layers. Chill cake in refrigerator for 30 minutes.

Remove from the refrigerator and spread Orange Frosting over the top and sides of cake. Gently sprinkle coconut on the top of the frosted cake.

In a double boiler, combine the egg yolks, sugar, lemon zest and juice. Cook over high heat, stirring constantly, until sugar dissolves. Stir constantly for about 20 minutes or until mixture thickens.

Add butter one pat at a time and incorporate into the lemon mixture. Cool filling completely before spreading on cake layers.

In a medium-sized bowl, cream softened butter until light and fluffy. Add the sugar, orange zest, and juices and beat until smooth. Stir in coconut. Spread the frosting over the entire cake.