Place onion slices in a lightly greased 1-quart casserole, and set aside.
Melt butter in a heavy saucepan over low heat; add flour, stirring until smooth. Cook 1 minute, stirring constantly. Gradually add chicken broth and milk; cook over medium heat, stirring constantly, until thickened and bubbly. Add salt, pepper, curry powder, paprika, and cheese; stir until cheese melts. Spoon mixture over sliced onions. Bake, uncovered, at 350° for 30 minutes.