Ham and Scalloped Potatoes

We seem to always have  ham and cheese from the cheese tray  left over from holiday dinners and this Thanksgiving was no exception.  I took some of that cheese and grated it and diced some of the ham and made a casserole for dinner. It was wonderful with a little salad!

5 medium potatoes sliced thinly, preferably on a mandoline
1  1/2 cups diced ham
4 cups grated cheese ( I used Colby and Jack)
1 cup sliced green onion
4 Tbl butter
2 Tbl flour
1  1/2 cups milk
1/4 tsp dry mustard
1/2 tsp white pepper

Boil the sliced potatoes in water for about 5 minutes to get them started.  Drain well and pat them dry.
In a sauce pan melt the butter, add the green onions, mustard and pepper.  Stir in the flour and cook for a minute or two to make a roux.
Slowly pour in the milk, stirring constantly and cook over medium heat until the mixture thickens up a bit.
In a buttered medium casserole dish, layer a third of the potatoes, half of the ham and a third of the cheese.  Repeat this step over the top. Add the remaining potatoes and then the cheese on top.
Pour the creamy milk mixture evenly over the casserole, cover and bake at 350 for one hour.  Remove the cover and continue to bake for 15 to 30 minutes until the potatoes are done and the top is lightly browned.