Wine-Braised Chuck Roast with Onions

Put oven rack in middle position and preheat oven to 325°F.
Pat beef dry and rub all over with 1 1/2 teaspoons salt and 1/2 teaspoon pepper. Heat oil in an ovenproof 5-quart wide heavy pot over moderately high heat until hot but not smoking and brown beef on all sides, about 15 minutes total. Transfer beef to a plate.
Add onions to pot and sauté over moderately high heat, stirring frequently, until pale golden, about 10 minutes. Add garlic, tomato paste, thyme, rosemary, and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper and cook, stirring, 2 minutes. Add wine and water and bring to a boil. Return beef to pot, then cover tightly and braise in oven, turning once after 1 hour, until beef is very tender, 2 1/2 to 3 hours total.
Let beef stand, uncovered, in onion sauce about 30 minutes.
If reserving some meat for beef salad , cut off one third of roast, and, when cool enough to handle, shred and toss with 3/4 cup onion sauce. Cool completely, uncovered, then chill in an airtight container.
While shredded beef cools, preheat oven to 350°F and transfer remaining beef to a cutting board and cut into 1/2-inch-thick slices. Season with salt and pepper and return beef to sauce. Reheat, covered, 20 minutes.