Preheat the oven to 450øF.

Rinse the bones well until the water runs clear – it's ok if there is some meat on them still. Pat dry with paper towels. Place the bones on a baking sheet and roast for about 30 minutes, or until deeply browned.

Place the bones in a very large stockpot and cover with water. Simmer for about an hour, skimming the surface occasionally to remove any foam.

Meanwhile, add the onion, celery, carrot, and tomato paste to a skillet. Cook until the vegetables are soft. Tie the spices up in a piece of cheesecloth.

Add the softened vegetables and the spices to the stockpot. Simmer for another hour or two, or until stock is rich and flavorful.

Strain and discard solids. Cool the stock quickly in a water bath, then move to the refrigerator. Once the stock has completely cooled, most of the fat will rise to the top and can be skimmed of and discarded if desired. The stock can then be divided into smaller containers and frozen for later use.