The first step in this recipe is to make a big pan of roasted veggies. The challenge is not eating most of them before you make the soup.
Heat the oven to 375. Scrub and then chop 2 lbs. of potatoes, 1 lb. of carrots, and 1 lb. of Beets. If you want a very smooth texture, peel the potatoes first.
Place all the vegetables in a large baking dish and drizzle generously with olive oil. Sprinkle with salt, pepper and 1/2 t. dried thyme. Roast until the vegetables are all very tender and caramelized, 30-40 minutes, stirring occasionally.
Trim the thin, leafy branches off 1 head of celery and reserve. Tear off 6 celery stems and wash carefully, then dice them. Peel and dice 1 onion. Saute the diced celery and onion in a heavy soup pot in 1 T. olive oil until very tender and just beginning to brown. Season generously with salt and pepper. Add 1 or more minced clove of garlic and cook another 2 minutes, then add 4 C. broth of your choice. Add 3 of the reserved celery branches and 1 Bay Leaf and bring to a boil, then lower to a simmer.
When the vegetables in the oven are done roasting, transfer them to a bowl. Use a ladle to spoon 1/2 C. of the simmering broth (or 1/2 C. white wine) to the roasting pan, then use a wooden spoon to deglaze the pan. Add the deglazing liquid back to the pot. Remove the celery and bay leaves.
Puree the soup in batches in a food processor or with a hand blender. Add 1 1/2 C. milk of your preference to the pot and bring back to a simmer.
Season with lemon juice, salt and pepper to taste.