Slice eggplants. From 2 eggplants you should be able to get about 18 (¼ inch-thick lengthwise) eggplant slices
Brush the eggplant slices with olive oil, season with salt and arrange a many as will fit on your broiler pan. Broil about 4-5 minutes on each side and repeat until all the slices are browned.
For Bolognese Sauce: Sauté the onion, garlic, carrot and celery in oil in a large skillet. Add beef to the sautéed vegetables, season with salt, and cook stirring frequently, until the meat has browned. Then, add tomato purée, tomato paste, a bay leaf, salt, and oregano to taste.
Assemble in Baking Dish: Next, grease a baking dish and spoon some sauce into the bottom of the baking dish. Place a tablespoon of beef bolognese sauce on the end of each eggplant slice, sprinkle with mozzarella and roll up. Place in baking dish, seam side down. Spoon more sauce on top and sprinkle with remaining mozzarella cheese. Cover and set in the refrigerator until you are ready to bake.
When you're ready to bake, preheat your oven to 350℉. Bake uncovered for 20 minutes until rollatini are heated through and mozzarella cheese melts.