Layer 1/2 of the potatoes and 1/2 of the onions in the casserole dish. Pour 1/2 of the cheese sauce over the potatoes. Layer the rest of the potatoes and onions and and pour the rest of the cheese sauce over. Top with the remaining reserved cheese. Cover with foil and bake for 30 minutes.
Uncover and bake for another 30 minutes or until it is nicely browned on the top and bubbly.
