Macaroni and Cheese

1 package elbow macaroni (2 cups)
3 Tbs butter
3 Tbs flour
2 cups milk
½ tsp salt
dash pepper
2 cups grated American cheese
tomato slices
 
Cook macaroni in boiling, salted water until tender; drain.  Melt butter, blend in flour; add milk and cook until thick, stirring constantly.  Add seasonings.  Add 1-1/2 cups cheese, stir until melted.  Put macaroni in greased 1-1/2 quart dish.  Pour sauce over; salt tomato slices and push edge into macaroni.  Sprinkle with remaining cheese.  Bake at 350º for 30 minutes.