Preheat oven to 325 degrees F.  In a large oven-safe pot or a Dutch oven, heat the olive oil and butter over medium heat.  Sear chuck roast on each side until a deep golden brown crust develops, about 3-5 minutes.  Remove roast from pot.  Add onion, celery, bay leaves, garlic, peppercorns, thyme and parsley to pot.  Stir and cook until onion is almost translucent.  Be careful to not burn garlic.

Add roast back to pan on vegetables.  Pour beef stock over the roast and season meat with salt.  Cover the pot with a tight fitting lid and put in preheated oven to cook for about 4 hours.  Check meat periodically and baste with pan juices.

When meat is tender to shred, use two forks to tear meat into bite-size chunks.  Continue to baste with juices to avoid drying out meat.  Add carrots to pot.  Cover and cook for another 45 minutes.   When carrots are tender, remove pot from oven.  Strain extra pan juices from meat.

To make gravy, combine extra juices with additional 2 cups of beef stock.  (Add additional water to create about 3 cups of liquid.) Bring to a boil in a medium saucepan.  Whisk in all-purpose flour, making a smooth gravy.  Pour over shredded pot roast.  Season with additional salt and pepper.  Serve with mashed or roasted potatoes.