Preheat your oven to 325°F (160°C).

In a large Dutch oven or heavy pot, heat the olive oil over medium-high heat. Season the chuck roast generously with salt and pepper, then sear it in the hot oil until browned on all sides, about 4-5 minutes per side. Remove the roast and set aside.

In the same pot, add the diced onion, carrots, and celery. Sauté for about 5-7 minutes, or until the vegetables are softened.

Return the chuck roast to the pot. Add the honey, balsamic vinegar, garlic cloves, fresh sage, and beef broth. Bring the mixture to a simmer.

Cover the pot with a lid and transfer it to the preheated oven. Braise for 3-4 hours, or until the meat is tender and easily pulls apart with a fork.

While the roast is braising, prepare the celeriac and potato gravy. In a medium saucepan, add the diced celeriac and potatoes. Cover with water, add a pinch of salt, and bring to a boil. Reduce heat and simmer until the vegetables are tender, about 15-20 minutes.

Drain the celeriac and potatoes and return them to the pot. Add the heavy cream and butter, then mash until smooth and creamy. Season with salt and pepper to taste.

Once the roast is done, remove it from the oven and let it rest for about 10-15 minutes before slicing.

Serve the sliced roast with the velvety celeriac and potato gravy on the side. Garnish with chopped fresh parsley if desired.