Sweet dumpling squash are a small, single-serving variety with a skin tender enough to eat. Here, they make edible bowls for rich vegetable stew.
Preheat oven to 375 degrees. Using a large knife or cleaver, slice off and reserve the top inch of each of 6 squash. Scoop out and discard seeds and stringy fibers. Arrange squash and their tops, cut sides up, in a small roasting pan. Brush insides of squash and tops with butter; sprinkle with 1 teaspoon salt. Place a thyme sprig in each squash. Bake until squash are very tender, about 1 1/4 hours.
Meanwhile, peel and halve remaining squash; remove and discard the seeds and stringy fibers. Cut flesh into 3/4-inch pieces; combine with parsnips, turnip, carrots, and potato. In a 5-quart Dutch oven, heat 2 tablespoons oil over medium heat. Add half the vegetables; season with remaining 1 1/2 teaspoons salt. Sear on one side until lightly browned, about 3 minutes. Using a slotted spoon, transfer to a medium bowl. Add remaining 1 tablespoon oil to pot. Repeat with remaining vegetables, and transfer to bowl.
Reduce heat to medium-low, and add onion and garlic. Cook, stirring occasionally, until onion is softened, about 15 minutes. Add ras el hanout, and cook, stirring, 1 minute more. Add tomatoes, and cook, stirring occasionally, until they have broken down and formed a thick sauce, about 15 minutes.