Fry the onion in the oil and butter in a large pan over a low heat for 5-10 minutes until soft and translucent.
Add the sliced mushrooms and garlic and cook over a high heat until the mushrooms are cooked and the excess liquid has evaporated.
Add the paprika, smoked paprika, thyme and flour and cook for a minute while stirring.
Add the white wine and cook until the liquid has mostly evaporated then gradually stir in the stock.
Add the bay leaf, mustard, soy sauce, worcestershire sauce and nutritional yeast then bring up to a simmer and cook for about 5 minutes until the sauce has thickened.
Stir in the creme fraiche and simmer for a few minutes then serve with pasta or rice.
