With a sous vide wand, heat about 6 liters of water in a large pot or container to 133°F / 56°C.
Meanwhile, heat the olive oil in a large skillet over high heat. When the oil begins to smoke, sear the chuck roast, holding the meat in place with metal tongs to form a golden crust all over. Remove the meat from the skillet and let cool.
Place the chuck roast into a Ziploc or vacuum-sealed bag, along with the pepper, garlic, thyme, butter, sugar and salt. Vacuum seal closed.
When the water reaches temperature, submerge the bag in the water, ensuring it’s completely covered. Cover the pot or container with plastic wrap to avoid water evaporation. Cook for 24 hours, up to 48 hours.
Towards the end of the sous vide time, preheat the oven to 350°F / 180°C.
In a baking dish, toss the potatoes, carrots, apples, and onions with the olive oil, salt, pepper and garlic powder, and mix everything together with your hands. Distribute the thyme stalks in between the vegetables. Roast for 45 minutes.
Meanwhile, in a medium pot, bring the broth to a simmer and reduce it to 1½ cups.
Remove the bag from the sous vide bath. Strain the liquid in the bag directly into the pot with the broth.
In a small cup, dissolve the cornstarch in 5 tablespoons cold water and whisk into the broth. Bring the gravy to a boil, mixing constantly. When boiling, cook for 1 minute, then remove the gravy from the heat.
When the vegetables are fork-tender, remove them from the oven and increase the temperature to 450°F / 230°C. Remove the thyme stalks from the vegetables.
Drizzle the sauce over the vegetables and stir. Place the sous vide chuck roast on top and return to the oven until the chuck has a deep golden brown color, about 5 minutes.
Top the roast with fresh herbs. Serve with a side of green beans if you like.