1. Preheat the oven to 400 degrees.
2. Peel the eggplant and slice crosswise into paper-thin slices. Blend or process the tomatoes in the container of an electric blender or food processor until smooth.
3. Butter a large casserole or baking dish and make alternate layers of eggplant, mozzarella, and tomato puree, making the top layer cheese. Bake for 45 minutes.