Step 1Heat the oven to 350 degrees. Grease and flour two 9-inch cake pans.
Step 2In a mixing bowl, combine the flour, baking powder and salt; set aside. Place the milk in a small bowl and stir in the vanilla; set aside.
Step 3Using a mixer, beat the butter at medium speed until creamy. Add the sugar and continue beating, stopping to scrape down the sides, until the mixture is light and evenly combined. Add the eggs, one at a time, beating well each time, until the mixture is thick and smooth.
Step 4Add about a third of the flour mixture to the batter and beat well at low speed. Add about half of the milk, beating well. Add another third of the flour mixture, followed by the rest of the milk and then the remaining flour mixture, beating well each time until the mixture is thick and smooth. Quickly scrape the batter into the cake pans, dividing it evenly. Bake until the cakes are golden brown, spring back when lightly touched in the center and begin to pull away from the sides of the pans, 25 to 30 minutes.
Step 5Remove the cake pans from the oven and leave on a wire rack for 10 minutes. Turn the cakes out onto wire racks or plates, then turn the layers top side up and allow to cool completely.
Step 1Place the sugar with one-half cup water in a small pan and stir to dissolve. Bring the mixture to a gentle boil and cook without stirring for 3 minutes. Then boil for 5 to 10 minutes more, stirring often, until the syrup has thickened and will form a thread about 2 inches long when poured from a spoon, or a candy thermometer reads 238 degrees. Remove from heat.
Step 2While the syrup is boiling, beat the egg whites in a large mixer bowl at high speed until they are bright white and shiny and pillow up into voluminous clouds. Pour the thickened syrup into the egg whites and continue to beat at high speed until the icing becomes fluffy and holds a peak, 4 to 5 minutes.
Step 3Place one cake top-side down on a serving plate. Spread the optional jam over it, then cover it generously with icing and sprinkle with coconut. Place the second layer on top of the first, top side up. Ice the sides of the cake to help keep it steady, then spread icing generously over the top, completely covering the cake.
Step 4Place the serving plate on a cookie sheet to catch any loose coconut and sprinkle coconut all over the cake. Gently pat handfuls of coconut onto the sides and top to cover bare spots.