Remove any membrane from the pork fillet and then cut into thin strips.
Season with salt and pepper.
Heat a large non stick frying pan until hot, add the oil and then add the meat. Fry until brown, but take care not to overcook. Remove from the pan leaving the juices behind and put to one side.
Add the butter to the pan, add the onions and cook over a low heat until the onions are tender. Add the paprika and stir in the mushrooms and leeks. Increase the heat again and cook for a minute or two.
Return the pork to the pan and add the buttermilk and heat through
Serve with mashed potatoes and veggies
Serve with buttery mashed potatoes and a selection of local veg and you're good to go!