Preheat your oven to 325°F (160°C).

In a large Dutch oven, heat olive oil over medium-high heat. Season the chuck roast with salt and black pepper. Sear the roast on all sides until browned, about 5-7 minutes per side. Remove the roast and set aside.

In the same Dutch oven, add the sliced leeks and cook until they are softened, about 5 minutes. Add the minced garlic and sauté for an additional minute until fragrant.

Pour in the balsamic vinegar, scraping the bottom of the pot to deglaze. Add the beef broth, chopped sage, and thyme. Stir to combine.

Return the seared chuck roast to the pot, ensuring it's submerged in the liquid. Bring the mixture to a simmer.

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

About 30 minutes before the roast is done, prepare the velvety celeriac gravy. In a pot, combine the diced celeriac with enough water to cover. Bring to a boil and simmer until tender, about 15-20 minutes. Drain and set aside.

In the same pot, add the heavy cream and butter. Using an immersion blender or a regular blender, puree the celeriac until smooth. Season with salt and pepper to taste.

Once the roast is finished, remove it from the oven and let it rest for 10-15 minutes before slicing. Serve the sliced roast drizzled with the fig-balsamic glaze from the pot and alongside the velvety celeriac gravy.