Pat the beef chuck roast dry with paper towels and season generously with kosher salt and black pepper.
Heat the olive oil in a large skillet over medium-high heat. Sear the roast for 4 to 5 minutes per side until a brown crust forms. Transfer the meat to the slow cooker.
Arrange the baby potatoes, carrots, and yellow onion around the seared beef in the slow cooker.
In a small bowl, whisk together the beef broth, tomato paste, Worcestershire sauce, and minced garlic. Pour this mixture over the beef and vegetables.
Place the fresh rosemary sprigs on top of the meat.
Cover the slow cooker and cook on LOW for 8 hours, or until the beef is fork-tender and pulls apart easily.
Carefully remove the beef and vegetables to a serving platter and cover with foil to keep warm. Discard the rosemary sprigs.
To make the gravy, pour the cooking liquid from the slow cooker into a medium saucepan. Bring to a simmer over medium heat. Whisk in the cornstarch and water mixture, stirring constantly for 2 minutes until the gravy thickens.
Pour the gravy over the pot roast and vegetables. Garnish with chopped fresh parsley before serving.