Spray slow-cooker bowl with nonstick
cooking spray. Season roast with salt,
thyme and black pepper. Place in bottom
of slow cooker.
Scatter onion, carrots, celery and garlic
over roast. Pour stock and balsamic
vinegar over top. Cover and cook on LOW
for 10 hours.
Remove roast and allow to rest 15
minutes before slicing. Skim fat from
cooking liquid. Mash vegetables in
cooking liquid to slightly thicken sauce.
Serve sliced roast with sauce and, if
desired, polenta and sautéed peppers.