Gluten Free Pot Roast with Root Vegetables

• 

  3 lb boneless beef chuck roast
• 1 ½ tsp kosher salt
• 

  1 tsp black pepper
• 

  2 tbsp olive oil
• 

  1 medium yellow onion, roughly chopped
• 

  3 cloves garlic, smashed
• 

  2 tbsp tomato paste
• 

  1 cup dry red wine
• 

  2 cups beef broth
• 

  1 tbsp tamari
• 2 sprigs fresh thyme
• 1 sprig fresh rosemary
• 

  2 bay leaves
• 

  4 medium carrots, cut into 2-inch pieces
• 

  2 medium parsnips, cut into 2-inch pieces
• 

  1 lb baby potatoes, halved
• 

  2 tbsp cornstarch
• 

  2 tbsp cold water

For serving

• 2 tbsp fresh flat-leaf parsley, roughly chopped (optional)