Step 1Heat the oven to 400 degrees. Put the cut-up bones in a single layer in a large roasting pan. Roast the bones about 2 hours. Stir the bones during the roasting process so they brown but do not burn.
Step 2During the last half-hour of cooking, add the onions, carrots and garlic.
Step 3After 2 hours, transfer the roasted bones and vegetables from the roasting pan to a large stockpot.
Step 4Pour off the fat from the roasting pan. Add enough water to cover the bottom of the roasting pan and stir to deglaze all the browned bits from the bottom of the pan. Pour the deglazing liquid over the bones in the stock pot. Add the remaining water to the stock pot.
Step 5Bring the water to a boil over medium-low heat, then reduce to a simmer and cook 2 hours. Skim the stock to remove any sediment while cooking. Skim off fat.
Step 6Add the bay leaves, thyme, peppercorns and tomatoes. Continue to simmer, loosely covered, 6 additional hours.
Step 7Strain the stock through a cheesecloth-lined strainer. Cool. Refrigerate overnight. Remove the congealed fat from the top of the stock and discard.
Step 8Warm the stock to liquid and ladle it into labeled and dated freezer bags. Lay the filled bags on a baking sheet and freeze so they can be easily stacked. Smaller portions of broth can be ladled into ice cube trays, silicone muffin pans or plastic pint cartons and frozen. Once frozen, they can be removed and put into plastic freezer bags for easy storage in the freezer.