Melt margarine in saucepan; add flour, salt, and paprika.

Stir until smooth; add milk slowly.

Cook over medium heat; stir until sauce thickens and boils.

Put half of potatoes in greased casserole. Add half of sauce. Repeat with remaining potatoes and sauce.

Cover casserole; bake at 350 degrees for 1 hour.

Uncover. Bake another 1/2 hour until potatoes are soft.