For the pot roast: Preheat the oven to 350 degrees F.
Sprinkle the beef chuck liberally with 1 tablespoon salt and 2 teaspoons pepper. Heat a large saute pan over high heat until it smokes. Add the grapeseed oil and allow the oil to heat for a few seconds. Carefully place the chuck in the pan and sear each side until browned (do not move the meat too much; it will release from the pan when it is ready to be moved). Transfer the meat to a roasting pan or ovenproof casserole dish.
In the saute pan, add the onions, carrots and celery and cook until the onions and carrots get some color, 8 to 10 minutes. Deglaze the pan with the red wine and allow the wine to simmer until the alcohol has cooked off, 2 to 3 minutes. Whisk in the tomato paste and then the beef broth and allow the cooking liquid to simmer for a few minutes to marry the flavors. Season with salt and pepper and then pour the cooking liquid over the roast in the roasting pan.
Cover the roast with a layer of plastic wrap and then a layer of aluminum foil. Cook until tender, 3 to 4 hours. Remove the roast from the oven and allow it to rest in the cooking liquid for 30 to 40 minutes.
For the pan jus: After the meat has rested, strain the cooking liquid and pour it back into a pan. Bring to a simmer and simmer until reduced to 4 cups.
Whisk together the cornstarch and 6 tablespoons water. Whisk the cornstarch slurry into the simmering cooking liquid and then cook the jus until it thickens to cover the back of a spoon. Season with pepper.
For the whipped potatoes: In a pot, cover the potatoes with cold water and bring to a boil. Cook until the potatoes are fork-tender. Drain the potatoes; set the strainer over the sink and allow the potatoes to steam for 5 minutes.
Pour the potatoes back into the pot, add the melted butter and sour cream and whip with a hand blender until smooth. Season with salt and white pepper.
Bring a pot of water to a boil; prepare an ice-water bath. Blanch the broccoli in the boiling water and then transfer to the water bath to stop the cooking process. Repeat with the carrots. Drain and set aside.
To plate: In a large saute pan, heat the grapeseed oil until it begins to smoke. Add the broccoli and carrots and saute for 3 to 4 minutes. Season with salt and pepper.
Divide the whipped potatoes among 6 plates. Slice the pot roast and place the slices on top of the potatoes. Ladle the pan jus over the pot roast. and then place the broccoli and carrots around the plate.