Preheat oven to 350 degrees. Grease or use cooking spray for a 2 lb. loaf tin. You can also line the bottom with parchment paper.
Cream the butter and sugar until well incorporated and fluffy (at least 2 minutes).
Add in the beaten egg slowly, followed by the self-raising flour, slowly.
Add in the grated lemon peel and salt until combined. Fold in the apples.
Pour batter into the loaf tin.
Combine the additional sugar, cinnamon, and nutmeg and sprinkle heavily on top of the loaf, so it forms a crust.
Bake for 50 minutes to 1 hour, making sure that the top is a rich brown and a toothpick comes out clean. The apples will adjust the texture of the cake, but there should be no moisture or batter showing on the toothpick.
Allow to cool for 15 minutes in the tin, and remove to a wire rack to cool completely. You can add additional lemon rind and more sugar mixture to the top of the cake as it cools.
Makes for a great Irish teatime, or wishing you were in Galway for breakfast!