Trim any large pieces of fat from the roast.
Pat the meat dry, then season with salt and pepper.
Let it sit at room temperature for 15–20 minutes if your kitchen is cool.
Heat the olive oil in a large, heavy pot over medium heat (see note 1).
When the oil is hot, add the chuck roast. Cook for 5–6 minutes until browned (see note 2).
Flip the roast and cook for another 5–6 minutes until browned on both sides.
Remove the pot from heat and transfer the roast to a plate or pan. Cover loosely with aluminum foil to keep warm.
Without washing the pot, return it to medium heat and add the onions, carrots, and celery. Cook for 5 minutes, stirring often, until the onions begin to soften.
Add the garlic and cook for 1 minute, stirring frequently.
Pour in the onion soup, stirring while scraping up any browned bits from the bottom of the pot.
Return the chuck roast to the pot along with any juices collected on the plate.
Add enough water to cover at least ¾ of the roast at its thickest part.
If the broth does not start simmering immediately, increase the heat. Once it reaches a simmer, lower the heat to medium-low, cover, and cook for 2½ hours, or until nearly fall-apart tender. Check every 30 minutes to ensure the liquid remains at a gentle simmer, adjusting heat as needed.
Add the potatoes to the pot, arranging them around the roast and ensuring they are submerged in the broth.
Raise the heat to bring the liquid back to a simmer, then lower it again to medium-low. Cover and cook for 20–30 minutes, until both the meat and potatoes are fork-tender. A fork or knife should slide in and out easily.
Serve the roast with potatoes and sauce, garnished with chopped parsley if desired. Enjoy with a green salad and a generous piece of crusty bread to soak up the rich, flavorful broth.