In a large bowl toss the oil with onions, carrots, garlic, leeks and arrange them in a roasting pan.
Place pan in oven and roast, stirring once, for 45 minutes or until golden brown and tender.
In a large saucepan or stock pot combine the roasted vegetables with carrot tops, thyme, rosemary, bay leaf, peppercorns, clove and water. Bring to a boil, reduce heat and simmer, stirring occasionally for 1 hour or until the broth is reduced to about 8 cups. Strain.
Additions for Summer Stock: summer squash, tomatoes, green beans, eggplant, bell peppers, corn cobs, marjoram, oregano, basil.
Instead of first roasting vegetables, saute them over high heat for 5 to 10 minutes or until vegetables begin to brown. Complete recipe as above.
Additions for Winter Stock: celery root, parsley root, dried sage, mushrooms (both dried or 1 pound fresh).