Cheesy Scalloped Potatoes

1/4 cup chopped onion
2 Tbsp. butter
2 Tbsp. flour
1 1/4 cup milk
1/4 tsp salt
1 cup shredded cheese, divided
3 medium potatoes, peeled and thinly sliced (3 cups)

In a sauce pan, cook onion in butter till tender. Stir in flour and salt. Add milk all at once. Cook and stir until thickened and bubbly. Remove from heat. Mix in 3/4 cup of cheese. Place half the sliced potatoes in a greased 1 quart dish. Cover with half the sauce. Repeat layers. Top with remaining 1/4 cup of cheese. Bake covered at 350 degrees for 35 minutes. Uncover and bake 30 minutes more or till potatoes are tender. Let stand 5 minutes. Serves 4. (If you don't want to use the cheese and just have plain scalloped potatoes, omit the cheese and increase the salt to 1/2 tsp.)