Step 1

Preheat oven to 400°F.

Step 2

Line a rimmed baking sheet with parchment paper. Arrange bones, onion, carrots, celery and garlic in a single layer; roast for 40 minutes.

Step 3

Transfer roasted bones and vegetables to slow cooker. Add peppercorns, vinegar and 12-16 cups cold water (depending on the size of your slow cooker). Cover and cook on low for 17 hours (or up to 24 hours).

Step 4

Let cool 30 minutes or more then strain out and discard large solids. Strain again through a fine sieve lined with cheesecloth (optional) into a large bowl or measuring pitcher. Transfer broth to lidded containers (such as lidded glass quart jars). Refrigerate overnight then skim fat from the top of the cold broth. Refrigerate for up to 3 days or freeze for up to 6 months (be sure to leave room at the top of your container to make room for the liquid to expand as it freezes).