Roasting the Bones: Preheat your oven to 400°F (about 200°C). Arrange the lamb bones on a baking sheet and roast for 30 minutes, until golden brown. This step enhances the broth's flavor.
Preparing the Broth: Transfer the roasted bones to a large stockpot. Add water to cover the bones by a few inches. Stir in the apple cider vinegar: this helps leach minerals from the bones into the broth.
Simmering: Bring the pot to a boil, then reduce the heat to maintain a low simmer. Skim off any foam or impurities that surface in the first few hours.
Cooking Time: Allow the broth to simmer gently for 24-48 hours. The long simmering time maximizes the extraction of flavors and nutrients from the bones.
Seasoning: In the last hour of simmering, season the broth with salt to taste.
Finishing the Broth: After the cooking time is complete, remove the pot from the heat. Strain the broth through a fine-mesh sieve, discarding the bones and any solid residue.
Cooling and Storing: Let the broth cool to room temperature. Refrigerate for up to 5 days or freeze for up to 3 months. A layer of fat may solidify on top when chilled, which can be removed if desired or left to enrich the broth.