1. For the roast: Preheat the oven to 350 degrees F. Place the carrots, celery, and onion in the bottom of a roasting pan. (Nadine uses the vegetables instead of a rack.) Add enough water to just cover the vegetables.
2. Cut four X's in the sides or top of the meat and push in the garlic pieces. Rub the entire roast with olive oil and then dredge it in steak seasoning.
3. Heat a large skillet over medium-high heat and sear all sides of the meat. Set the meat on top of the vegetables, cover the pan with foil, and roast until a meat thermometer inserted in the meat registers 130 degrees F for medium-rare, about 2 hours. Transfer the roast to a cutting board and let it rest for 30 minutes.
4. To make the gravy : Strain the roasting-pan juices; discard the vegetables. Melt the butter in a skillet over medium-high heat. Whisk in the flour. Stir in the roasting pan juices and the demiglace, and simmer until thickened.
5. Slice the roast beef very thin. Put the slices in the gravy. (Nadine likes to smother the beef in the gravy.) Plate up the sandwiches with the meat between two slices of white bread and ladle more of the gravy on top. Serve with mashed red potatoes.
From Guy Fieri's More Diners, Drive-Ins and Dives book. Adapted from a recipe courtesy of Nadine S. Voelker of Nadine's Bar and Restaurant.