Beef Stroganoff

Slice the beef sirloin into thin strips. Chop the onion finely. Slice the mushrooms.

Heat 1 tbsp of vegetable oil in a large pan over high heat. Add the sliced beef in batches and sear quickly until browned on all sides, about 1-2 minutes per batch. Season with half of the salt and half of the black pepper. Remove the seared beef from the pan and set aside.

Add the remaining 1 tbsp of vegetable oil and the butter to the same pan. Add the chopped onion and sliced mushrooms. Sauté over medium heat until the vegetables are softened and lightly browned, about 7 minutes.

Sprinkle the flour over the sautéed vegetables and stir well for 1 minute to cook out the raw flour taste. Gradually whisk in the beef broth, ensuring no lumps form. Bring the mixture to a gentle simmer and cook for 5 minutes, or until the sauce slightly thickens.

Reduce the heat to low. Stir in the sour cream and Dijon mustard until thoroughly combined and smooth. Return the seared beef (and any juices) to the pan, stirring to coat. Heat gently for 2-3 minutes, ensuring the sauce does not boil, which can cause the sour cream to curdle. Taste and adjust seasoning with the remaining salt and black pepper as needed. Serve hot.