Cut the round loin meat off of the bones, into bite-sized pieces, and set aside.
Place the bones in a cast-iron skillet, and salt liberally. I used two skillets.
Roast bones for 30 minutes, flipping them half-way through.
Place the bones in the pressure-cooker (or just use a stove top if you like – but it will take twice as long) along with 3 cloves of crushed garlic, 2 sprigs of rosemary, and the chopped onion. Cook on high (meat setting) for 2 one-hour cycles.
Strain liquid into a stove-top soup pot, and reduce down by 50%.
Chop anchovy fillets, and combine with tomato paste and remaining crushed garlic. Set aside.
Saute’ the lamb pieces in olive oil on medium-low heat for 8-10 minutes or until browned.
Add the tomato paste mixture and combine. Cook for another 3-4 minutes.
Add a cup of red wine to the lamb mixture. Scrape all the bits off the bottom of the pan, and add it all to the stock pot (which should now be reduced by 50%).
Turn the stew down to low heat, cover, and walk away for an hour.
Add butter and cream, stirring until completely combined.
Take stew off the heat and let rest for 2-3 minutes.
Sprinkle in xanthan gum while whisking. When it’s completely combined, return to a boil for 30 seconds while stirring, then reduce heat to low.