In a large pan, heat the olive oil over medium high heat. While the oil is warming up, dry the beef in paper towels. (If the beef is damp, it won't brown!) Gently saute the beef until browned on all sides.
Add the browned beef to your slow cooker. Add the onion, garlic, salt, pepper, Pinot Noir, Beef Stock, tomato paste, and thyme. Make sure the beef is completely covered (add water if necessary)
Cover and cook on low for 8 -9 hours. With 1.5 hours, remaining, add the mushrooms. I don't add the mushrooms till later in the cooking process, because I like them to be slightly firm.
When the beef is nice and tender, remove the meat and vegetables from your slow cooker and keep warm. In a small bowl, add flour or cornstarch to 1/4 cup stock, wine, or water and whisk until combined. Add to the remaining sauce and stir to thicken.