Heat the oil and butter together in a frying pan or skillet.
Fry the onion until very soft (and starting to brown on the edges).
Add the garlic, and fry for a minute or two.
Throw in the mushrooms and cook until nice and soft.
Add the Worcestershire sauce (or mustard), tomato puree (paste), paprika and seasoning. Stir and cook for a couple of minutes.
Pour in the stock and continue to cook until it starts to bubble.
Reduce the heat to very low, and slowly add the Greek yoghurt (this will prevent splitting, but if it does happen, it's no big deal - the taste is not impaired in any way).
Cook for about 10 more minutes, then remove from the heat. Sprinkle a little fresh thyme (or any other herb). Serve with mashed potatoes, pasta or rice. Enjoy!
