Prepare lemon mix as per box.
Use a stand mixer. beat the egg whites and salt on high speed until foamy.
With the mixer still running, slowly add the sugar. Beat mixture until soft peaks form (when you pull the mixer out of the white mixture you should get a little point that bends over).
Bring the corn syrup to a boil over medium heat in a small saucepan. When the corn syrup comes to a boil, remove from heat. Slowly pour the hot corn syrup into the egg mixture while your mixer is mixing on high. Beat the mixture until stiff peaks form, about 5 minutes. Add the vanilla and mix to combine.
When cakes and lemon are cool, Stack cakes on serving plate, with a layer of lemon between each cake. Cover cake with frosting, top with coconut.
Use the frosting right away and eat any leftovers, as it doesn’t store well. You can leave a cake that has been iced with this uncovered, since any type of plastic wrap on it will be a mess. Add the coconut as soon as you are done spreading the icing.