Cut the carrots, celery root, turnips, parsnips, potatoes, and squash into 1‐in. (2.5‐cm) dice.
Place these cut vegetables, plus the shallots and garlic cloves, in a baking pan.
Pour the olive oil over the vegetables and sprinkle with the thyme, salt, and pepper. Toss or mix until the vegetables are well coated with oil. Add more oil if necessary.