Preheat oven to 360°. (Yes, that temperature is correct.)
Sift flour, salt, and baking powder together in a small bowl. Set aside.
Put milk and butter together in a sauce pan over low heat. Cook until it reaches the boiling point. The mixture should be very hot and just starting to boil, but don’t allow it to overcook. Remove from heat.
Put sugar in the mixing bowl. Add eggs one at a time, beating thoroughly after each. Add vanilla and mix thoroughly. Add flour mixture gradually, mixing well.
Add the hot milk and butter mixture to the flour and eggs mixture all at once. Mix well.
Pour into prepared cake pans and bake for 20 minutes. Remove from oven and allow to sit about 10 to 15 minutes in the pan. The cake tends to crisp around the edges and stick to the pan, so run a knife around the edges to loosen the cakes while they are still warm. Remove from pans, peel off the wax paper, and cool on a rack overnight.
Day 2: Frosting and Assembly
Mix together sugar, cream of tartar, and water in a saucepan. Bring to a boil without stirring, until the mixture spins a 6-inch thread (about 240° to 242°). Keep the pan covered for the first 3 minutes of cooking to prevent crystals from forming on the sides of the pan.
Beat two egg whites in a large glass mixing bowl until stiff. Pour the hot syrup very slowly into the egg whites, beating constantly on high speed. Add vanilla. Continue beating until mixture is fluffy and will hold it shape and is cool and thick enough to spread of sides and top of cake. You do not want runny frosting.
Frost cake in layers and sprinkle the top and sides with shredded coconut. Press the coconut into the frosting so that it sticks. Put in a cake keeper and refrigerate. Will keep for up to a week in the refrigerator. The cake actually tastes even better if you allow it to sit for 24 hours because the frosting starts to absorb into the cake.