Preheat oven to 425 degrees F. Line two baking sheets with foil. Coat one with olive oil and spread the roughly chopped onion, carrots, and celery. Spread the beef bones and pork bone out on the other baking sheet. Cook in oven for 45 minutes.

In a large stock pot, combine bones, vegetables, water, peppercorns, and bay leaf.

Heat the mixture on medium heat until the liquid begins to release steam and turn the heat down to low before it just about comes to a boil.

Continue to cook without allowing it to boil for 10-12 hours, skimming any foam or "skum" off the top.

Allow to cool for about an hour. Remove bones and vegetables and strain through a fine wire mesh.

* If you want to remove the fat, go ahead and do this now by skimming it off. I recommend keeping it.

Ladle into sterilized canning jars and store in refrigerator or freeze.

Your stock will last about 4 days in the fridge and 4-6 months in the freezer.