Heat up the oil in a pan over a medium heat, add the butter and allow it to melt.
Add the sliced mushrooms, and give a good stir.
Leave to cook for about 5 minutes, stirring occasionally, until the mushrooms have released their liquid and are brown.
Add the onion and garlic, and cook for a further 2-3 minutes until the onion has soften.
Remove from the pan and set aside.
Add the remaning oil and butter, then add the chicken and leave to cook for 6-7 minutes or until cooked through and lightly brown.
Add the mushrooms back to the pan together with the chicken stock, tomato puree, bay leaf and seasoning, and leave to cook for 2-3 minutes.
Before adding the sour cream to the pan, mix one tablespoon of the hot liquid from the stroganoff at a time in order to bring the cream at the same temperature to avoid curdling.
6-7 tablespoons should be enough, before pouring it into the pan.
Give a good stir, add the parsley, and remove from the heat.
Serve with rice, pasta or mashed potatoes.