Place the beef stew meat, flour, and salt in a large plastic bag. Shake until the beef is coated. Heat olive oil in a skillet over medium high heat and brown the beef on all sides, then transfer the meat to the slow cooker.
Melt the butter in the same skillet and cook the sliced onions until they become soft. Add the minced garlic and cook briefly until fragrant. Transfer the onion mixture to the slow cooker. Pour the red wine into the skillet and scrape up any browned bits, then add this liquid to the slow cooker.
Add the potatoes, carrots, dried parsley, black pepper, onion soup mix, and beef broth to the slow cooker. Stir gently so the ingredients are evenly combined.
Cook on high for 30 minutes, then switch the slow cooker to low and continue cooking for about 6 hours until the beef is very tender.
Stir together the warm water and flour to make a slurry. Pour the mixture into the stew and cook uncovered for about 15 minutes until the broth thickens.
Garnish with fresh thyme if desired and serve warm.
