Start by placing the beef stew meat in a resealable plastic bag. Add the all-purpose flour and seasoning salt to the bag, then shake it until the meat is evenly coated.
Heat the olive oil in a skillet over medium-high heat. Once hot, add the floured stew meat to the pan and brown it on all sides. Use a slotted spoon or tongs to remove the meat and place it at the bottom of a slow cooker. Season with black pepper.
In the same skillet where you browned the meat, sauté the diced onion for 2 minutes. Don’t worry about cleaning the skillet in between; those browned bits are added flavor! Transfer the onions into the slow cooker with the meat.
Now, pour in the Worcestershire sauce, water, and beef demi-glace (or Swanson Flavor Boost) into the skillet. Whisk until everything is mixed, making sure to scrape up any browned bits from the bottom of the pan. Turn off the heat and set it aside.
Add the diced red-skinned potatoes, sliced carrots, celery, and bay leaves to the slow cooker with the meat and onions.
Pour the broth/Worcestershire mixture from the skillet into the crockpot as well.
Cover the slow cooker and set it to cook on low for 8 hours.
Before serving, make sure to remove the bay leaves.
