1. Preheat oven to 300° F.

2. Place chopped onion, brown sugar and thyme in a small food processor. Pulse until finely pureed and no large pieces of onion remain. Set aside.

3. Trim chuck roast of excess surface fat if necessary. Use two pieces of cooking twine to truss and stabilize the roast. (See video) Sprinkle salt and pepper on all sides of the roast.

4. Heat a 12 inch braising pan or 4-5 quart dutch oven over medium heat and add canola oil. Add roast to hot pan and press down to create good contact. Cook, without moving, for approximately 5-7 minutes on the first side until deeply browned. Flip and cook for an additional 5-7 minutes on the second side. Remove roast from the pan and transfer to a large plate. Set aside.

5. Add pureed onion mix to the hot pan with beef drippings. Sauté onion puree, stirring frequently until mixture begins to brown and thicken. Stir in whole grain mustard.

6. Add hard cider and stir to deglaze, scraping up any browned bits. Add chicken stock, stir and bring to a boil. Reduce to a simmer and continue to simmer (uncovered) for 5 minutes.

7. Carefully return beef and accumulated juices back to the pan. Cover and transfer to a preheated oven and bake for 3 hours total. Flip beef over halfway through cooking.

8. After 3 hours, a paring knife should easily slide into the roast. Remove pot from oven and cool for two hours before transferring to the refrigerator to chill over night.

9. When ready to serve, remove the chilled roast from the refrigerator.

10. Use a fork to remove all of the fat solidified on the surface of the braising liquid.

11. Transfer the roast to a cutting board, remove the cooking twine and cut the roast into 1 inch thick slices. Set aside while you finish the sauce.

12. Return the pot with the braising liquid to the stovetop. Heat on medium heat until the braising liquid just starts to steam.

13. In a small bowl, mix together flour and softened butter to form a smooth paste. Whisk butter/flour paste into steaming braising liquid until completely dissolved. Bring to a simmer and stir frequently (uncovered) for 5 minutes until thickened. Properly thickened sauce will leave a brief trail in the bottom of the pan when you drag a silicone spatula through it.

14. Taste for seasoning and add more whole grain mustard if desired.

15. Nestle cold sliced beef into hot sauce, cover and heat on medium low for 5 minutes. Use tongs to flip each slice of beef over. Cover and simmer on medium low for 5-10 more minutes or until beef is heated through and sauce is bubbling.

16. Serve with mashed potatoes and roasted root vegetables if desired.

(This dish is best enjoyed when it is first finished (day two of cooking). To reheat after day 2, add 1-2 Tbsp of additional hard cider to the sauce before covering and reheating gently on medium low heat.)