If browning the beef, add a drizzle of olive oil to a heavy pan and set over medium high heat. Salt and pepper both sides of the pot roast and brown in the hot oil. Cook for about 5 minutes per side or until nicely browned.
While the roast is browning, place the carrots, celery and onions in the slow cooker. Top with the potatoes and sprinkle with salt and pepper.
Place the beef (either browned or not) on top of the potatoes and nestle in the bay leaf.
If you browned the beef, pour the red wine (or beef broth if you're not using wine) into the pan and cook for about 2 minutes, using a wooden spoon to scrape up the browned bits. Pour this over the beef in the slow cooker.
Cook on low for 6 to 8 hours.
If you'd like to thicken the sauce, mix 1 tablespoon of cornstarch with two tablespoons of water and stir into the sauce in the crockpot about 30 minutes before serving.
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Notes
You can use boneless beef or bone in. Browning the beef is optional, but it does add more depth of flavor. Red wine is optional, you can deglaze the pan with the beef broth.