Begin by dredging the beef stew meat in all-purpose flour seasoned with salt and pepper. Sear the beef in batches in a skillet over medium-high heat until golden brown.

In the same skillet, add oil if necessary, and sauté the onion, garlic, and cremini mushrooms until translucent and fragrant.

Transfer the beef and sautéed vegetables into the slow cooker. Add beef broth, Worcestershire sauce, and Dijon mustard. Stir to combine.

Cover and cook on low for 7-8 hours or on high for 4-5 hours until the beef is fork-tender.

Stir in sour cream off the heat until incorporated, adjusting seasoning with salt and pepper before serving.

Serve over cooked egg noodles or cauliflower mash, garnished with fresh herbs or paprika.