Peel eggplant and cut into 1/2" thick slices.
Cover bottom of buttered 2-qt. casserole with eggplant slices.
Top with layer of tomato slices, then onion.
Season to taste.
Sprinkle with part of cheese;
dot with part of butter.
Repeat layer by layer until casserole is filled,
ending with tomatoes topped with cheese.
Cover casserole.
Bake 375F, 45 min. 4 servings.