Position a rack in the center of the oven and heat the oven to 350°F.Season the beef with 1 tsp. salt and 1/4 tsp. pepper and then toss in a large bowl with 2 Tbs. of the flour. Heat 1 Tbs. of the butter and the oil in a 5-1/2- to 6-quart Dutch oven over medium-high heat. Cook half of the beef until browned on several sides, about 5 minutes. Using a slotted spoon, transfer the beef to a plate. Repeat with the remaining beef. Melt 2 Tbs. of the butter in the pot. Add the leeks, carrots, celery, and a pinch of salt, reduce the heat to medium and cook, stirring occasionally, until softened, about 10 minutes. Add the wine and cook, scraping up any browned bits with a wooden spoon, until evaporated, 7 to 8 minutes. Stir in the remaining 3 Tbs. flour and cook for 1 minute.Whisk in 5 cups of the broth. Stir in the barley, bay leaves, sage, nutmeg, 1/2 tsp. salt, and the beef along with any accumulated juices. Bring to a boil. Cover the pot snugly with foil and then a tight-fitting lid and braise in the oven until the beef is almost tender, about 1 hour. Stir in the squash and the remaining 1 cup broth. Cover with the foil and lid and continue braising until the beef and squash are very tender, about 30 minutes more. Remove and discard the bay leaves from the stew, and then stir in the parsley and half-and-half. Season to taste with salt and pepper.