Preheat oven to 400 degrees F.

In a large bowl, toss olive oil with quartered onions, quartered carrots, crushed garlic cloves, and trimmed leeks.

Arrange the vegetables in a roasting pan.

Roast in the preheated oven, 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 sprig, rosemary sprig, bay leaf, black 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 the stock to remove solids.