Place tomatoes, leek, onion/scallions, mushrooms, celery, and carrots in a large mixing bowl or on cookie sheets that have been sprayed with olive oil cooking spray.
Sprinkle with 1-2 tablespoons salt and 1 tbsp. pepper (more of each if desired).
Drizzle 1/3 to ½ cup olive oil over top.
Stir to combine or just lay out on cookie sheets.
Spread all the vegetables onto one or two large cookie sheets that have been sprayed with olive oil cooking spray.
Roast vegetables in a 400° oven about 30-45 minutes.
(Meanwhile, cut the tops off the garlic bulb and place in a pan.
Drizzle with a little olive oil over top.
Roast the garlic at the same time as the vegetables.
Once vegetables are done place in large stockpot (or crockpot, see below), with all the drippings from the pan.
Add seasonings and one quart vegetable stock.
Bring to a boil and then reduce heat and simmer until seasonings blend about 30 minutes.
Stir in additional vegetable stock, if desired.
Check seasonings.
Add more basil if desired.