Preheat oven to 350 degrees.
Pat dry chuck roast and season generously with salt and pepper. Dredge the roast in flour on all sides and shake off the excess
In a large dutch oven, add some oil over medium heat and sear the roast on all sides for a few minutes so that it gets nice and golden. Set to the side.
In the same pot, add chopped red onion and the white and light green parts of the leek. Sautée for 3 minutes. Stir in the tomato paste and cook out for another 2 minutes. Throw in the garlic.
Deglaze with cabernet wine and beef stock then bring up to a bubble. Reduce the heat to low, add the chuck roast back in along with the thyme and bay leaves. Cover and throw into the oven for 3 hours.
After 2.5 hours, add some chopped carrots to the dutch oven to soften up for the last 30 minutes.
Remove the veggies and herbs, and skim out any impurities and extra oil in the sauce. Reduce the sauce over medium heat for a few minutes while whisking. Serve over mashed potatoes and greens, pouring the reserved sauce on top to finish it off.