Preheat oven to 180°C / 350°F. Wash all vegetables. Slice a thin cap off the top of each tomato and bell pepper and reserve. Halve the zucchinis lengthwise and scoop out centers with a small spoon, leaving about 6–8 mm (1/4"–1/3") shell. For eggplants, halve lengthwise or roast whole then halve depending on size — for small eggplants: halve lengthwise and scoop out centers leaving a 6–8 mm shell. For tomatoes, carefully scoop pulp and seeds into a bowl, reserving pulp for the sauce. Finely chop the scooped-out flesh from all vegetables and set aside. Lightly salt the inside of each hollowed vegetable and place them upside down on a rack to drain while you make the filling (10–15 minutes).

Dice the onion finely (this is separate from the shallots in the filling) and set aside to sweat with the vegetable scrap if using.

Filling

Soak breadcrumbs

Put the breadcrumbs in a bowl and pour the milk over them. Let soak for 5 minutes, then squeeze lightly to combine into a moist paste.

Cook aromatics

Heat 3 tbs olive oil and 1 tbs butter in a wide skillet over medium heat. Add the minced shallots and cook 2–3 minutes until softened. Add the minced garlic and the finely chopped reserved vegetable flesh and diced onion, cook 4–5 minutes until softened and most moisture has evaporated.

Brown the veal

Increase heat slightly and add the ground veal, breaking it up with a spoon. Cook until just browned — about 6–8 minutes. If the veal releases excess liquid, cook until it evaporates. Deglaze with the white wine, scraping up browned bits, and let the alcohol burn off (about 1–2 minutes). Remove the pan from the heat and let cool slightly.

Combine filling

In a large bowl combine the cooked veal mixture, soaked breadcrumbs, chopped parsley, thyme, grated Parmesan, egg, salt, pepper, and a pinch of nutmeg if using. Mix thoroughly until homogenous and slightly sticky. Taste a small spoonful (cook a tiny pinch in a pan if you prefer) and adjust seasoning.

If the filling feels too wet to hold its shape, add up to 2–3 tbs additional breadcrumbs. If too dry, add 1–2 tbs milk.

Assembling & Braising

Fill vegetables

Lightly oil a baking dish that will hold the vegetables snugly. Using a spoon, pack the veal filling into each hollowed vegetable, pressing gently so the filling is compact but not over-compressed. Mound the filling lightly above the rim to allow for shrinkage. Replace the reserved tops (caps) where appropriate.

Make sauce and bake

In a bowl combine the tomato passata/crushed tomatoes, reserved tomato pulp, stock, sugar, bay leaf and 1 tbs olive oil. Season lightly with a little salt and pepper. Pour enough sauce into the bottom of the baking dish to come halfway up the sides of the vegetables (about 120 ml), reserving the rest to top during baking. Cover the dish tightly with foil and bake in the preheated oven for 30 minutes. After 30 minutes remove foil, spoon some of the remaining sauce over the tops, reduce oven to 170°C / 340°F and continue baking uncovered for another 20–25 minutes until the filling is cooked through (internal temp ~70°C / 160°F) and vegetables are tender.

If the tops begin to brown too quickly, loosely tent foil for the final minutes of baking. For a gratin finish, sprinkle additional grated cheese on top and broil for 2–3 minutes at the end.

Finishing

Rest and serve

Remove from oven and let rest 5–10 minutes. Discard the bay leaf. Garnish with fresh basil leaves and a drizzle of good olive oil. Serve warm with pan juices spooned over or alongside crusty bread or polenta.