Melt the butter in a non-stick pan over medium high heat.
Mix in the flour and cook for about 1 minute
Add the milk, nutmeg, white pepper, salt, and garlic.
Stir until the mixture has become the consistency of tomato sauce
Remove from heat.
Spread the sauce onto your dough. Add your corned beef and cabbage.
Set your oven to the highest temperature it will go without burning your house down (500 degrees to me).
Bake until the crust has browned around the edges. About 15 minutes in my oven.
Allow to cool for at least 5 minutes before slicing.