How to Make It
In a large saucepan, cover the veal and beef with the stock. Add the bay leaves, parsley and thyme, season lightly with salt and black pepper and bring to a boil over moderate heat. Reduce the heat to low, cover partially and simmer until the meats are very tender, about 2 hours for the veal and 3 1/2 hours for the beef. As the meats are done, transfer them to a bowl and let cool slightly. Discard the bones and gristle. Cut the meats into 1-inch pieces. Strain the cooking liquid into a bowl; you should have about 2 cups.
Preheat the oven to 350°. Cut the tops off the pumpkins and reserve. Scrape out the seeds and season the insides with salt and pepper. Add 1 tablespoon of butter and 1/4 cup of milk to each pumpkin, cover with the top and set on a rimmed baking sheet. Bake for about 1 1/4 hours, or until the pumpkins are just tender. Cover with foil and keep warm on the baking sheet. Alternatively, halve the acorn squash lengthwise and scrape out the seeds. Season the squash with salt and pepper and fill the centers with the butter and milk. Transfer the squash to a large baking dish and roast, cut side up, for about 30 minutes, or until tender; keep them warm in the dish.
In a large skillet, heat 1 tablespoon of the olive oil. Add the pancetta and cook over low heat, stirring often, until crisp, about 5 minutes. Stir in the scallions and transfer the mixture to a plate.
In a medium saucepan of boiling water, cook the corn until tender, about 5 minutes; drain.
In a large saucepan, heat the remaining 1 tablespoon of olive oil. Add the onions and bell pepper and cook over low heat until softened, about 10 minutes. Add the crushed red pepper and cook, stirring, for 1 minute. Add the meats and their cooking liquid, the pancetta mixture and corn and simmer until heated through, about 4 minutes. Season with salt and black pepper.
Spoon the stew into the pumpkins or squash. Cover the pumpkins with the tops, or cover the squash with foil; bake until heated through, about 20 minutes for the pumpkins and 10 minutes for the squash. Bring the stew to the table in the pumpkins, then spoon the stew into bowls, scooping out the pumpkin flesh. Alternatively, serve each guest a stew-filled squash half.