Preheat the oven to 350 degrees F. Combine all ingredients in a large roasting pan. Cover and bake 75-90 minutes, or until vegetables are very tender. Puree the vegetables, with a little added water, in 2 to 3 batches in a food processor. Place in a heatproof casserole dish. Cover and return to oven for 10-15 minutes more, or until hot.
Note: Vegetables can be prepared hours advance, allowed to cool, and then stored in the fridge. Reheat, covered, in the oven or microwave.