Preheat the oven and season the roast

• Preheat the oven to 165 °C.
• Pat the chuck roast dry with paper towels.
• Rub the roast with olive oil, then season evenly with the salt, onion powder, garlic powder and black pepper.

Sear the beef

• Heat a large Dutch oven over medium-high heat.
• Add the seasoned chuck roast and sear for 3–4 minutes per side, until deeply browned.
• Remove the roast and set aside.

Soften the vegetables

• Reduce the heat to medium and add the butter to the same pot.
• Add the onion and celery and cook, stirring occasionally.
• Add the minced garlic, dried rosemary and dried thyme and cook until fragrant.

Build the sauce

• Stir in the tomato paste and flour and cook, stirring constantly, until the flour is incorporated and the tomato paste begins to caramelize slightly.
• Pour in the Worcestershire sauce and about a quarter of the broth, scraping the bottom of the pot thoroughly with a wooden spoon to loosen all the browned bits.
• Pour in the remaining broth and stir until everything is well combined.

Braise the roast

• Return the seared chuck roast to the pot; the broth should come roughly a third of the way up the sides of the meat.
• Bring the liquid to a gentle simmer, then cover the Dutch oven tightly with the lid or foil.
• Place the covered pot in the oven and cook at 165 °C.

Flip and continue braising

• Carefully remove the pot from the oven and flip the roast so the other side sits in the broth, adding a little more broth if needed to maintain the liquid level.
• Cover the pot tightly again and return it to the oven.

Add the vegetables

• Remove the pot and add the carrots and baby potatoes around the roast, pushing them down into the broth as much as possible; add a little more broth if the liquid level is low.
• Cover the pot again and return it to the oven until the carrots and potatoes are fork-tender and the roast is very tender and easily pulls apart with a fork.
• If the roast is still firm once the vegetables are tender, remove the carrots and potatoes and continue cooking the roast, covered, in 20–30 minute increments until it reaches a fall-apart texture.

Make the gravy

• Remove the beef and vegetables from the pot and set aside.
• Bring the remaining liquid in the pot to a gentle simmer.
• Whisk together the cornstarch and cold water, then slowly whisk the slurry into the simmering liquid until the gravy reaches your desired thickness, stirring constantly.

Make the garlic thyme mashed potatoes

• Boil the peeled, diced russet potatoes with the whole head of garlic in salted water until fork-tender, then drain.
• Mash the potatoes with the roasted garlic cloves, butter, heavy cream, dried thyme, onion powder, garlic powder, salt and black pepper until smooth and creamy.

Rest and serve

• Let the roast rest before shredding or slicing.
• Serve the beef, vegetables and thickened gravy over a bed of mashed potatoes.