Slice eggplants evenly. Sprinkle with salt. Let rest ten minutes. Pat dry gently.
Preheat the Oven
Preheat oven to 375°F. Lightly grease a baking dish with olive oil.
Cook the Eggplant
Heat olive oil in skillet. Cook eggplant slices until lightly golden. Remove and set aside.
Cook the Onion
Add chopped onion to skillet. Cook until soft and slightly golden.
Add Garlic
Add minced garlic. Stir and cook for thirty seconds until fragrant.
Add Tomatoes
Pour crushed tomatoes into skillet. Add oregano, basil, salt, and pepper. Simmer ten minutes.
Layer the Dish
Place eggplant slices in baking dish. Spoon tomato sauce evenly over the top.
Add Cheese
Sprinkle Parmesan and mozzarella evenly over the eggplant and sauce layers.
Bake the Gratin
Bake uncovered for thirty minutes until cheese is melted and lightly golden.
Rest and Serve
Remove from oven. Let rest five minutes. Garnish with fresh basil before serving.
Notes
Use firm eggplants for best texture. Do not skip salting eggplant. Use fresh cheese for better melting. Add red pepper flakes for heat. Let gratin rest before serving. Bake until cheese is golden, not burnt.