Don't be alarmed by the amount of liquid you add to the vegetables. It looks like too much, but it's not. Trust me, it will absorb and thicken into a lovely gravy-like sauce. I think fresh marjoram is absolutely perfect here, but you could also use fresh thyme or a teaspoon or so of dried marjoram, thyme, or oregano.
3 tablespoons extra-virgin olive oil
3 tablespoons unsalted butter
1 red onion, cut into 1-inch pieces
3 medium carrots, cut into 1-inch rounds
1 medium celery root, peeled and cut into 1-inch pieces
1 acorn squash, peeled and cut into 1-inch pieces
2 garlic cloves, finely chopped
1 cup dry white wine
3 tablespoons tomato paste
3 cups water (or veggie or chicken stock)
1 tablespoon chopped fresh marjoram
Kosher salt and freshly ground black pepper
2 cups all-purpose flour
1 teaspoon kosher salt
1 tablespoon plus 1 teaspoon baking powder
6 tablespoons cold unsalted butter, cut into small cubes
1 to 1-1/3 cups heavy cream
1-1/2 teaspoons finely chopped garlic
Pinch of coarsely ground black pepper
1/2 cup grated sharp Cheddar cheese (not shredded--you want small flecks)
Heat the oven to 400°F. In a large sauté pan, heat half of the oil and half of the butter over medium-high heat. Add the onions, carrots, and celery root, and cook, stirring occasionally, until the vegetables are browned, about 7 minutes. Transfer the cooked vegetables to a 13x9-inch casserole dish or roasting pan. Melt the rest of the oil and butter in the hot skillet. Add the acorn squash and sauté until lightly browned, about 7 minutes. Stir in the garlic and cook for another couple of minutes, then add to the casserole dish.
Increase the heat to high and add the white wine, tomato paste, and water (or stock) to the sauté pan. Bring to a boil, scraping up the browned bits stuck to the bottom of the pan, lower the heat, and simmer for about 3 minutes. Add this liquid to the casserole, sprinkle with marjoram, and season with salt and pepper to taste. Cover with aluminum foil and bake until the vegetables are just tender, about 30 minutes.
While the vegetables are baking, make the topping. In a food processor, whiz together the flour, salt, and baking powder until combined. Add the butter cubes and pulse until the mixture resembles a coarse meal (20 to 30 pulses). Empty the contents into a bowl and stir in 1 cup of cream, garlic, and pepper. If the mixture is too dry, add more cream. Mix in the grated cheese just until it holds together. Let rest. (You can also make the biscuits by hand, cutting in the butter with two knives or a pastry cutter.)
Remove the veggies from the oven and take off the foil. Using a large spoon, dot the surface of the vegetables with Ping-Pong ball-sized dollops of biscuit dough. The topping should be lumpy and bumpy. Return the casserole to the upper third of the oven and bake, uncovered, until the topping is cooked and browned, about 25 minutes. Let cool 10 minutes before serving.
Source: Adapted from Bistro Cooking at Home by Gordon Hamersley and Joanne McAllister Smart.