Season the chuck roast with the steak seasoning and place in the fridge, uncovered, overnight (this helps to tenderize the meat and keep the juices in).
Heat a sous vide water bath to 135F degrees.
Place the chuck roast in a vacuum seal bag and remove all the air. The water displacement method can also be used (see above in post).
Place in the water bath and cook for 24-36 hours. (I cooked for about 26 hours and it still had a nice bite. The longer you cook it, the softer it will become).
Remove from the sous vide and place in an ice bath if you don't plan on eating it right away.
If you plan on serving it immediately, remove the beef from the bag and reserve the juices in a bowl.
Heat a large skillet or grill over high heat until smoking and brown the chuck roast for about 60-90 seconds per side, until a browned crust has formed. (Be careful not to overcook it).
Remove and set aside while making the gravy.
Heat the butter and flour in a saucepan over medium heat until a paste forms. Cook for about 1 minute, stirring constantly.
Add the sherry and cook another 30 seconds, stirring constantly.
Slowly pour in the bag juice and bring to a simmer. If the mixture is still too thick, add some beef broth until a gravy consistency forms.
Taste and season with salt (if needed) and serve alongside the chuck roast.
Slice the roast and serve with the gravy.