In a large frying pan heat the oil, add the leek and sauté for 2-3 minutes until just softened. Transfer to a plate.
Add the pork to the hot pan and fry quickly for 5 minutes until lightly browned. Add the paprika and mushrooms and cook for a further 2 minutes. Then add the wine and allow the liquid to reduce for 3 minutes.
Meanwhile, mix the sour cream and mustard together. Add this mixture to the pork, stir, then return the leeks to the pan and mix in. Cook for 2-3 minutes until the sour cream has thickened. Sprinkle over the tarragon and season with black pepper. Serve immediately, with rice, mash or pasta.
