Preheat oven to 375F. Spray 2 quart baking (9 x 12 inch) inch with non-stick spray, and set aside. In small pot, melt margarine, stir in flour, salt and pepper until smooth. Stir in milk. Bring to a boil, stirring frequently. Boil 2 minutes until thickened, stirring constantly.
Add cheese and chives. Stir until cheese is melted. Arrange potatoes slices in baking dish. Spoon cheese mixture over potato slices. Cover with aluminum foil and bake 45 minutes. Remove foil and bake 15 minutes more until potatoes are tender and top is golden brown. Let stand about 10 minutes, then serve hot.
Cajun Country -- New Iberia, Louisiana