Choose a 2-quart soufflé or gratin dish or four individual 2-cup casseroles. Roll out the pastry between and ¼ inch thick and cut it to fit the dish. Cut out leaves or other decorative shapes from the scraps. Refrigerate the pastry until needed. Have the béchamel cooking in a double boiler while you prepare the vegetables.
Toss the squash in flour, letting the excess fall away. Heat the oil and butter in a large skillet and add the squash and shallots. Sauté over medium heat until browned and tender, 20 to 30 minutes, stirring occasionally so that they color evenly. Transfer to the baking dish.
Peel the celery root, dice it into 1-inch cubes, and put them in the bowl with the juice plus water to cover. Parboil the remaining vegetables in salted water until tender but still a little firm. Drain, then parboil the celery root for 1 minute. Combine all the vegetables, season with salt and pepper, and transfer the stew to the dish. Tuck in the thyme sprigs.
Mix the béchamel and cream or milk and pour it over the vegetables, allowing the sauce to fall between the cracks. Refrigerate if baking later, then bring to room temperature before baking.
When ready to bake, preheat the oven to 425°F. Remove the pastry from the refrigerator and lay it on top of the vegetables. Brush the top with egg; add any decorations and glaze them, too. Bake for 12 minutes, then lower the heat to 350°F and continue baking until the crust is golden and puffed and the sauce is bubbling, 15 to 20 minutes more. Let settle for a few minutes, then serve.
About this recipe
Reprinted with permission from The New Vegetarian Cooking for Everyone, copyright 2014 by Deborah Madison. Published by Ten Speed Press, an imprinting of Penguin Random House LLC. Book cover illustrations copyright 2014 by Yana Beylinson.