1-First, start by heating about one-eighth inch of olive oil in a large skillet over medium heat to get that perfect golden crust on your eggplant. Slice the eggplant into half-inch or three-eighths-inch thick slices, then cook them in the oil without overlapping for even browning. Season each side with salt and pepper, flipping until they’re tender and nicely browned, then drain on paper towels and add more oil as needed to keep things going smoothly.

2-Next, in the same skillet, cook the chopped onion in the remaining oil until it’s soft and translucent, which takes just a few minutes. Add the fresh plum tomatoes or canned chopped tomatoes, along with a bit more salt and pepper, and let it simmer for 10 to 15 minutes until the sauce thickens into a rich, flavorful base. This step builds the heart of your eggplant Parmesan gratin, blending those fresh tastes into something truly special.

3-Preheat your oven to 400 degrees Fahrenheit (about 200 degrees Celsius) to get ready for baking. In a baking dish, layer the cooked eggplant slices, tomato sauce, and grated Parmesan cheese, repeating two or three times for a hearty stack. Bake for about 15 minutes until the cheese melts and bubbles, then garnish with chopped parsley if you like, and serve it hot or at room temperature for the best experience.