In a 6-quart slow cooker, add potatoes, carrots, and thyme sprigs.

Dry the surface of the chuck roast with a paper towel. Evenly season all sides of the beef with 1 ½ teaspoons salt and 1 teaspoon pepper.

Heat a large skillet over medium-high heat. Add oil. Once hot, add the beef to the pan. Sear until golden brown, about 5 minutes per side. Transfer to the slow cooker. Reserve the pan and drippings to cook onions.

Heat the skillet over medium heat. Add the onions, and saute until lightly golden and tender, about 2 minutes. Add garlic and saute for 30 seconds. Add balsamic vinegar and cook until reduced and coats the onions, about 1 minute. Add tomato paste, stir and cook for 1 minute. Transfer the mixture to the slow cooker.

Heat the skillet over medium-high heat. Add butter and flour, whisk to combine, and cook for 30 seconds. Gradually add beef stock, vigorously whisking to create a smooth and lightly thickened sauce, about 1 to 2 minutes. Stir in soy sauce and ½ teaspoon salt. Taste and adjust the seasoning as needed.

Add the pan sauce to the slow cooker. Cover and cook on the High setting for 4 to 5 hours or the Low setting for 7 to 8 hours. The vegetables should pierce easily with a fork, and the meat should be tender when sliced.

Look for the grainline, and cut the beef perpendicular across the grain into slices. Optionally, cut the slices further into smaller pieces. Return the meat to the slow cooker to keep warm before serving.

Serve pot roast with vegetables and sauce. Garnish with parsley.