Baked Ham and Spinach Au Gratin

3 T. butter
1 c. frozen chopped onions, thawed and drained
3 cloves garlic, minced
3 T. flour
1 1/2 t. dry mustard
2 c. milk
1 c. shredded cheddar, swiss, or monterey jack cheese
10 oz. pkg. frozen chopped spinach, thawed and drained
1/4 t. black pepper
1 lb. 4 oz. refrigerated shredded potatoes or frozen hash browns, thawed
1 lb. ham, cut into 1/2" cubes

Preheat oven to 375°. Melt butter in medium saucepan over moderate heat. Add onions and sauté, stirring occasionally, for 2 to 3 minutes or until pale golden. Add garlic and sauté for 2 to 3 more minutes. Blend in flour and mustard, then gradually whisk in the milk. Cook, stirring constantly, until thickened and smooth (about 3 to 5 minutes). Add cheese, stir until melted. Remove from heat and mix in spinach and pepper. Arrange half the potatoes in a lightly-greased 12x7 dish, then pour on half spinach mixture and scatter ham on top. Top with remaining potatoes and spinach mixture. Cover with foil, set on a baking sheet, and bake for 30 minutes. Remove foil and bake for an additional 15 minutes, or until potatoes are tender.

Serves 4 to 6.