1. Preheat the oven to 430°F.

2. Arrange the bones out on a large oven tray and cook in the oven for 45 minutes, turning the bones after 30 minutes.

3. Remove the tray once the bones are dark golden on all sides.

4. In the meantime, heat the olive oil in a large pan and caramelize the chopped onion, celery, garlic, and mushrooms over high heat.

5. Add the bones and the rendered fat from the tray into a large stockpot. Scrape the tray of all the lovely charred bits into the stockpot and tip in all the caramelized vegetables.

6. Add 175 oz (5 liters) of cold water to the pot and bring to the boil, skimming off foamy impurities.

7. Place a lid on the pot and reduce to a low simmer for 1 hour.

8. Remove the pan from the heat and strain the stock into a large clean pan.

9. Allow to stand until sufficiently cooled, then cover with cling film and place in the fridge overnight. The next morning, it will be easier to pick off the thick layer of fat that sits on the surface.

10. You will notice the broth is quite gelatinized when chilled. Tip the mass into a large pot and reduce over moderate-high heat to 20 fl oz. This can take a long time, so keep the lid off and check on it regularly.

11. For part two (which is the finishing of the sauce and should be started once the broth has reduced): Heat the olive oil in a pan and cook the sliced onions until softened and caramelized.

12. Add the red wine to deglaze the pan and cook until all moisture has evaporated.

13. Sprinkle over the arrowroot powder and stir well to coat the mixture.

14. Add the reduced, warm stock to the pan and add the thyme and rosemary.

15. Cook until the sauce has reduced and coats the back of a spoon.

16. Discard the herbs and serve the onion gravy over pork sausages.

17. Enjoy your Gluten-Free Sausage Gravy over any kind of meat, smashed potatoes, anything your heart desires!