Pat the chuck roast completely dry with paper towels. Season generously on all sides with kosher salt and black pepper.

Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Carefully place the roast in the hot skillet and sear for 4-5 minutes per side, until a deep brown crust forms. Transfer the seared roast to the crockpot.

Reduce the skillet heat to medium. Add the onion wedges and cook, stirring occasionally, for 3-4 minutes until they begin to soften. Add the minced garlic and cook for 1 more minute until fragrant.

Pour about 1/2 cup of beef broth into the skillet to deglaze, scraping up any browned bits from the bottom of the pan with a wooden spoon.

Place the chopped potatoes and carrots in the bottom of the slow cooker. Place the seared roast on top.

Pour the onion, garlic, and pan drippings over the roast. In a bowl, whisk together the remaining 2.5 cups of beef broth, Worcestershire sauce, soy sauce, and tomato paste. Pour this mixture into the slow cooker. Tuck the fresh thyme and rosemary sprigs alongside the roast.

Cover and cook on LOW for 8-10 hours or on HIGH for 4-5 hours, until the roast is fork-tender.

Carefully remove the roast and vegetables to a platter and tent with foil to keep warm. Strain the cooking liquid from the crockpot into a medium saucepan, discarding the herb stems. Skim any excess fat from the surface.

Bring the liquid to a simmer over medium heat. In a small bowl, whisk together the cornstarch and cold water to form a smooth slurry.

Slowly whisk the slurry into the simmering liquid. Continue to cook, whisking constantly, for 2-3 minutes until the gravy thickens. Season with salt and pepper to taste. Serve the pot roast with vegetables and drizzle generously with gravy.