Trim excess fat, cut beef chuck roast into 1-inch cubes, then season generously with salt and pepper.

Place beef cubes, sliced mushrooms, chopped onions, and minced garlic in the slow cooker.

In a bowl, whisk together beef broth, Dijon mustard, Worcestershire sauce, and flour until smooth, then pour over ingredients.

Cover and cook on low for 7–8 hours (or high for 4–5 hours) until the beef is melt-in-your-mouth tender.

Stir in sour cream and gently heat for another 10 minutes.

Spoon the creamy beef stroganoff over cooked egg noodles and sprinkle chopped parsley on top.