Spread the softened butter all over the bottom of your crockpot. Add the stewing beef and toss it with the cornstarch to coat evenly.
Add the mushrooms, onion, garlic, salt, pepper, Worcestershire sauce, Dijon mustard, and beef broth. Stir everything well to combine.
Cover and cook on high for 4 hours or low for 6 hours. Stir occasionally if you’re around, but it’s okay to let it cook undisturbed.
About 10 minutes before the beef mixture is done cooking, boil your egg noodles on the stove according to package directions. Drain and set aside.
When the cook time is finished, stir in the sour cream until fully combined. Then, gently fold in the hot, cooked egg noodles.
Let the stroganoff sit in the crockpot with the lid on for an extra 5 minutes. This helps the sauce thicken up beautifully.
Serve hot, garnished with parsley or chives if desired, and enjoy!
