Heat up half of the oil in a large frying pan over a medium heat.
Season the pork chunks with salt and pepper, and fry them on both sides until golden - work in batches to avoid overcrowding the pan.
Remove the pork from the pan and set aside.
Add the butter to the pan and allow it to melt.
Cut the mushrooms into quarters, and fry them until they release their liquid.
Remove the mushrooms from the pan and set aside.
Add the remaining oil, and fry the peeled and chopped onion and garlic until golden.
Return the pork and mushrooms to the pan, pour in the chicken stock and give everything a good stir.
Add 2-3 tablespoons of the hot liquid to the sour cream and mix well.
Remove the pan from the heat briefly, add the sour cream to it, give it a good stir, then return the pan to the heat.
Place a lid to the pan and leave everything to cook for 2-3 minutes.
Garnish with freshly chopped parsley and serve hot.