Preheat oven to 325°F.
Sprinkle roast with 2 ½ teaspoons of the salt and ¾ teaspoon of the pepper.
Heat oil in a large Dutch oven over high.
Add roast to Dutch oven, and cook until browned on all sides, about 14 minutes.
Transfer to a plate; set aside.
Reduce heat to medium-high.
Add onions and remaining 1 teaspoon salt and ¼ teaspoon pepper, and cook, stirring often and scraping up browned bits from bottom of Dutch oven, until onions begin to brown and soften, 6 to 8 minutes.
Add garlic, carrots, and mushrooms to Dutch oven.
Place roast on top of vegetables, and add wine, rosemary, and bay leaf.
Bring to a simmer.
Cover and transfer to preheated oven.
Bake 1 ½ hours.
Uncover and add potatoes.
Cover and bake until roast and potatoes are tender when pierced with a fork, about 1 more hour.
Let roast stand 15 minutes.
Remove rosemary and bay leaf.
Using 2 forks, separate meat into bite-size pieces.
Serve with vegetables.
