Slow Cooker Pot Roast

olive oil, (divided)

chuck roast*

Salt and freshly ground black pepper

medium yellow onion, (peeled, halved and cut into thick slices)

garlic cloves, (minced (1 1/2 Tbsp))

cup beef broth

Worcestershire sauce

minced fresh thyme

minced fresh rosemary

lbs small yukon gold potatoes, (left whole)

medium carrots (about 1 lb), (peeled and cut into 1-inch pieces*)

cornstarch mixed with 3 Tbsp beef broth, (optional, for thickening gravy)

chopped fresh parsley