Preheat the oven to 325˚F.
Heat a drizzle of oil in a Dutch oven or oven-proof braising pan set over medium-high heat and brown the beef, seasoning with salt and pepper.
Add the stock to the pan along with the tomato paste, cover and braise for 2 1/2—3 hours, or until the meat is very tender.
Cut the potatoes into large chunks, cover with water and bring to a simmer; cook for 15-20 minutes, or until very soft.
Drain, return to the warm pot and add the Boursin and milk, and season with salt and pepper to taste. Roughly mash, adding more milk or cream as needed.
Serve the braised beef over the potatoes, sprinkled with parsley.