In a large skillet, heat olive oil over medium-high heat.
Add beef strips and sear until browned on all sides, about 3-4 minutes. Transfer beef to the crockpot.
In the same skillet, add chopped onion and minced garlic. Sauté for 2-3 minutes until softened.
Add sliced mushrooms and cook for another 4-5 minutes until they release their moisture and begin to brown.
Sprinkle flour over the mushroom mixture and stir well to coat. Cook for 1 minute to remove raw flour taste.
Slowly pour in beef broth while stirring to avoid lumps. Add Worcestershire sauce, Dijon mustard, smoked paprika, salt, and black pepper. Stir to combine and bring to a simmer for 2 minutes.
Pour the mushroom sauce over the beef in the crockpot. Stir gently to combine.
Cover and cook on low for 6 hours until beef is tender.
About 20 minutes before serving, cook egg noodles according to package instructions. Drain and set aside.
Stir sour cream into the crockpot mixture until fully incorporated. Do not boil after adding sour cream to prevent curdling.
Serve beef stroganoff over cooked egg noodles and garnish with chopped fresh parsley.