Instructions

1. Preheat oven to 430 F (220 C) to roast the beef bones.  Roast for 45-60 minutes until the bones are golden brown.
2. Place a large pot on high heat and sauté the onion, celery, garlic, and mushrooms in the olive oil on high heat until they’re browned.  Then add in the roasted bones and fill up the pot with cold water (4 liters).
3. Bring to a boil, remove any impurities and then place a lid on the pot and simmer for 2 hours.
4. Then remove the lid and reduce the stock down to 20fl oz (600 ml) – this can take a while, so keep the lid off and check on it regularly.
5. In a separate, clean pan, melt the ghee and cook the sliced onions until softened and caramelized. Sprinkle over the arrowroot powder and stir well to coat the onions.
6. Add the reduced stock to the pan – as well as the thyme and rosemary – and cook until the sauce has reduced and thickened sufficiently to coat the back of a spoon.
7. Pick out the herbs and serve the sauce immediately, seasoning with salt and and freshly ground black pepper if necessary.