Prep onions, carrots and potatoes and place into cold crockpot.
Dry stew meat as best as you can using paper towels. Sprinkle with salt, pepper and flour and toss to coat evenly. Brown meat in batches, using a large, heavy-bottomed skillet and olive oil. Cook over medium high heat to form brown crust, but not to cook thoroughly. As meat browns, transfer over to crockpot.
Once all meat has browned, de-glaze pan with about 2 cups of beef broth and pour into crockpot. Top with remaining broth, bay leaves, Worcestershire sauce, thyme and more salt and pepper.
Cover and turn crockpot to high. Cook 4-5 hours or until meat is very tender and carrots and potatoes are fork tender. Remove bay leaves and thyme sprigs.
How to thicken Beef Stew:
In a small bowl, stir butter with flour and cornstarch until a smooth paste is formed. Spoon the butter-flour paste into the crockpot and stir gently to melt and spread it evenly though the contents of the crockpot. Cover and cook another 20 minutes to thicken completely.
Taste and adjust seasonings as needed. Stir in chopped parsley if desired. Serve hot.