Heat a skillet over medium-high heat and add a touch of oil. Once hot, add chunks of beef sirloin or chuck, searing for about 5 minutes until browned on all sides. Transfer the beef to your crockpot, leaving any fond behind in the skillet.

In the same skillet, reduce the heat slightly and add chopped onion and minced garlic. Sauté for about 3 minutes, until the onion is soft and translucent, and the garlic is fragrant. Once done, scoop the mixture into the crockpot, combining it with the seared beef.

To the crockpot, add sliced mushrooms, beef broth, Worcestershire sauce, Dijon mustard, salt, and black pepper. Mix well to ensure all ingredients are evenly distributed.

Cover the crockpot and set it to low for 6 hours or high for 3 hours. You’ll know it’s ready when the beef is tender and easily pulls apart with a fork.

About 30 minutes before serving, mix together sour cream and all-purpose flour in a small bowl until smooth. Stir this mixture into the crockpot, cooking uncovered for the remaining time to allow the sauce to thicken.

Prepare egg noodles or rice according to the package instructions in a separate pot. Once cooked, drain and set aside.

Ladle generous portions of the beef stroganoff over the hot noodles or rice. If desired, sprinkle with freshly chopped parsley for a vibrant touch.