Prepare and bake cake in a 13 x 9 pan according to package directions.

After taking cake out of oven, poke several holes all over cake with the handle of a wooden spoon.

Pour lemon curd over cake and spread it out evenly over top of cake and into holes.

Allow it to set and cool for about an hour.

Make frosting: Set up a double boiler on stove by bringing 1 inch of water to a simmer over medium high heat in a medium sauce pan. Top pan with a heat proof bowl. Make sure that water does not touch bottom of pan.

Add sugar, egg whites, cream of tartar, salt, and water to the bowl. Beat with an electric mixer for 1 minute. Carefully remove the bowl from heat and continue to beat for 7 minutes.

Frost cake with icing. Top with shredded coconut. Refrigerate until ready to serve.

For Homemade Lemon Curd: Set up a double boiler on stove by bringing 1 inch of water to a simmer over medium high heat in a medium sauce pan. Do not top with heat proof bowl yet. Measure lemon juice and add water to make sure liquid measures 1/3 cup. Whisk sugar and egg yolks until smooth in heat proof bowl. Add lemon juice and zest and whisk until smooth. Once water reaches simmer, reduce heat to low and place heat proof bowl on top making sure water does not touch bottom of pan. Whisk mixture until thickened about 8 minutes. Mixture should coat the back of a wooden spoon once thickened and will be pale yellow. Remove from heat and begin whisking in butter one tablespoon at a time allowing it to melt before adding another. This can be made ahead of time and stored in refrigerator for up to 2 weeks. Place plastic wrap directly onto surface of lemon curd before storing.