Place the lamb bones, vinegar, onion, carrots, garlic, bay leaf, and peppercorns in a large pot, slow cooker, or Instant Pot.
Pour in just enough filtered water to barely cover the bones and aromatics. Avoid adding too much water, as this will dilute the flavor and result in a less gelatinous broth.
If cooking on stovetop, cover and bring to a boil over high heat. Reduce the heat to low and simmer gently for at least 3 hours. Slow cooker: Cover and cook on Low for at least 8 hours. Instant Pot: Seal and cook on High Pressure for 3 hours, then allow the pressure to release naturally.
Once the cooking time is up, the bones should be softened and the connective tissue should break down easily. Let the broth cool until it is warm but no longer hot, then strain it through a fine-mesh sieve into jars or freezer-safe containers. For a clearer broth, strain it a second time through cheesecloth.
Refrigerate the broth for several hours or overnight. As it cools, the gelatin will set and the broth should become thick and gelled.
Once chilled, remove as much of the solidified fat from the top as you like. You can save the fat for sautéing vegetables. If you're not using the broth right away, you can leave the fat layer on top until you're ready to use it.
Keep the broth refrigerated and use within 3–4 days, or freeze it for longer storage. Use lamb bone broth in soups, stews, sauces, gravies, or simply replace the water with broth when cooking rice.