Preheat oven to 450°F. Place bones and carrots on a baking sheet and roast for 20–30 minutes, until browned.

Meanwhile, set Instant Pot on sauté and add oil and lamb meat scraps. Cook for 2–3 minutes and turn off the sauté function.

Place roasted bones and carrots in the Instant Pot with the meat scraps. Cover with 4 1/4 cups of water. Add celery, onion, and herbs; stir. Ensure liquid doesn’t go above the maximum fill line on your Instant Pot.

Place lid on Instant Pot and set the valve to sealing; cook for 2 hours on high pressure. Manually release pressure when it beeps and allow it to cool for a few minutes so that it’s not too hot to handle. Strain broth into a wide, shallow container (see safety note).

Place into a large jar, cover, and keep in the refrigerator overnight. The next day, skim the fat from the top of the broth and pour broth into containers for storing (see storage note).

Preheat oven to 450°F. Place bones and carrots on a baking sheet and roast for 20–30 minutes, until browned. Place roasted bones and all the solid ingredients into a large stockpot. Submerge in water so 2–4 inches of liquid is above ingredients, and ensure that there are a few inches between the top of the liquid and the top of the pot.

Bring to a boil, skim the surface, and remove the fat pooling at the top every 20 minutes until it boils. Once it does, lower the heat. Simmer, covered, for at least 12 hours and up to 24. Check periodically and continue to add water to ensure the level does not drop below the top of the bones. Strain liquid and follow instructions above for storing.