2-3 tablespoons vegetable or canola oil
4 pounds Chuck Roast
1 medium to large yellow onion, chopped
1/3 cup balsamic vinegar
2-3 tablespoons Dijon mustard
5 sprigs fresh thyme
2 cups reduced-sodium beef broth
2 bunches small carrots, with tops (cut off tops leaving a small stub)
1 pound very small baby potatoes, white or red
kosher salt & freshly ground black pepper