Place meat in large plastic bag or large container with cover. Combine 1/4 cup flour with salt and pepper; pour into the bag or container with the beef, secure, and then shake to coat.
Heat olive oil in a large skillet over medium-high heat. Add stew meat and cook until the meat is evenly browned.
Transfer the beef to a slow cooker along with the baby carrots, potatoes, celery, and thyme.
In a saucepan, boil 2 cups of beef stock on high heat. Stir in dry onion soup mix and Worcestershire sauce. Remove from heat; pour into the slow cooker.
In the same skillet used to brown the beef, melt the butter and sauté the onions over medium-high heat until softened. Add minced garlic and cook until fragrant.
Pour red wine into skillet and stir to loosen browned bits in the pan. Remove from heat, and pour the mixture into the slow cooker.
Cover and cook on low for 7 hours.
Prepare the slurry: in a small bowl, whisk 1 tablespoon of flour with 1/4 cup cold water.
Stir the slurry into the prepared stew and cook uncovered for 15 minutes, or until stew thickens. Serve and enjoy!
A slurry is a 1:4 ratio of flour, cornstarch, or arrowroot to cold water that is whisked together in a small bowl until blended. It is similar to a roux used to thicken soups.