Remove the tops and bottoms of the eggplants. Cut them in half lengthwise to create eggplant boats.
Place the eggplants in a big bowl with cold water and soak them for 30 minutes. You may place a plate on top to weigh them down. The soaking helps remove the bitter flavor from eggplants skin.
Preheat oven to 230°C / 446°F.
Drain the eggplants and place in a casserole dish. Score them with a knife creating deep criss-cross lines to help the eggplants bake well in the center. Take the 1 cup of olive oil and using a spoon, add spoonfuls of the oil on each eggplant.
Season the eggplants with kosher salt and freshly ground pepper.
Bake for 30 minutes until nicely roasted on top. Meanwhile, start preparing the tomato sauce.
Heat the splash of olive oil in a skillet over medium heat. Add the garlic and the onion slices and cook until completely softened.
Stir in the tomatoes and season with some kosher salt, ground pepper, and ground nutmeg. Cook for about 10-15 minutes stirring occasionally, until tomatoes start to drain and become mushy. Add the tomato paste and cook for 2 minutes more stirring occasionally.
Using a fork press the eggplants a bit to make some space for the sauce to sit on. Add spoonfuls of the sauce on the eggplant boats. Reduce heat to 160°C / 320°F and slow-cook the eggplants for about 35 minutes. Then raise the temperature again to 200°C / 392°F and roast the eggplants for about 10-15 minutes more.
Serve with chopped fresh parsley on top.