Sprinkle the chuck roast with flour that has been generously seasoned with salt and pepper.
Place olive oil in a skillet over high heat, until nearly smoking hot. Add floured beef, and brown on both sides, about 5 minutes. (You can also do this right in the crock of many modern slow cookers by using the cooker’s browning function.)
Remove skillet from heat, and then deglaze the pan with the beef stock, scraping any browned bits from the bottom.
Transfer beef and all liquid from the skillet to a slow cooker and top with the vinegar, garlic, thyme, bay leaves, salt, and pepper, tossing all to combine.
Place the potatoes, onion, carrots, and celery on top. Set the cooker to LOW, cover, and let cook 7 hours.
Whisk cornstarch into 2 tablespoons of water and stir into the cooking liquid. Re-cover, set the cooker to HIGH, and let cook 1 additional hour or until meat is fork-tender.
Turn off heat, stir in butter, and serve roast smothered with the vegetables and gravy.
Set the cooker to LOW, cover, and let cook 2 hours, stirring halfway through.