Place the onions, carrots, celery, leek tops, garlic, parsley, thyme, bay leaves, salt, pepper, and water in a large pot and bring to a boil over high heat (If 12 cups of water won’t fit in your pot, you can use 10). Reduce the heat and simmer gently, covered, for 1 hour.

Strain and discard the vegetables. Season to taste and use in your favorite soup recipes.