In a large skillet, melt 1 tbsp butter over medium-high heat. Add the beef and cook until browned, about 4-5 minutes. Remove the beef from the pan and set aside.
In the same skillet, melt the remaining butter. Add the onions and mushrooms, and sauté for 5-7 minutes, until the mushrooms release their moisture and the onions soften.
Sprinkle the flour over the mushroom mixture and stir well to coat. Cook for 1-2 minutes to form a roux.
Gradually whisk in the beef broth and bring to a simmer. Cook for 3-5 minutes until the sauce thickens slightly.
Stir in the sour cream, Worcestershire sauce, Dijon mustard, paprika, salt, and pepper. Cook for another 2-3 minutes.
Add the cooked beef back into the skillet and stir to combine. Let it simmer for an additional 3-5 minutes to heat through.
Serve the beef stroganoff over a bed of cooked egg noodles.