Season the roast with salt and pepper. Put the flour in a large bowl, add the roast and toss to coat evenly. Set an electric pressure cooker to "brown" according to the manufacturer's instructions and warm the olive oil until nearly smoking. Add the roast and brown on all sides, 3 to 4 minutes total. Transfer the roast to a platter. Add the onions to the pressure cooker and cook until tender, 3 to 5 minutes. Return the roast to the pressure cooker along with the carrots, stock, garlic, thyme and bay leaf. Cover, set the pressure to "high" and cook for 1 hour and 20 minutes. Release the pressure according to the manufacturer's instructions. Transfer the roast to a cutting board, cover loosely with aluminum foil and let rest for 5 minutes. Slice the meat and arrange on a warmed platter. Remove the thyme and bay leaf from the sauce. Transfer the vegetables to the platter. Skim the fat from the sauce and season with salt and pepper. For a thicker sauce, leave some of the vegetables in the sauce and puree using a blender or stick blender. Transfer the sauce to a warmed sauceboat and pass at the table. This recipe yields 8 servings.