1. Heat a heavy-based cast iron pot, add some oil and begin to brown the beef cheeks all over.  
2. Now add the onion, garlic, carrots and mushrooms, allow to colour. 
3. Add the butter to increase the browning of the meat, the more colour achieved here, the better the final  flavour of the braise. 
4. Drain off any excess fat, then add the red wine, followed by the demi-glace and the tarragon. Make sure the cheeks are completely covered. Place a lid on the pot. 
5. Cook in a preheated oven at 130c for 2 hours until tender. 
6. Remove the cheeks from the braise, pass the liquid into a separate pan. 
7. Add the cheeks to this pan and reduce the stock over high heat, basting the cheeks until a thick sticky glaze in achieved 
8. Finish the glazed cheeks by adding Maldon salt, crispy onion, chives and grated horseradish. 

For the mash: 

1. Place the potatoes on a bed of salt on a tray. Bake at 200c for 1 hour in a preheated oven.  
2. Add the milk and cream together and heat in a small saucepan. 
3. Remove the potatoes from the oven, cut in half and press through a fine sieve or potato mouli, leaving the skins behind. 
4. Place the potato pulp in a pot on the heat and add the cream/milk in stages. Finally, ass the diced cold butter until a shiny mash is achieved. 
5. Season and serve warm.