Place the fish on a plate. Mix the flour, salt, pepper and thyme together and sprinkle over the fish. Turn the fish over a few times to coat it in the flour.
Heat the butter and oil in a frying pan and fry the fish flesh side down for 2–3 minutes until golden. Turn over and fry for further 3–4 minutes until cooked through. Transfer to plate and keep warm.
Add the wine to the pan and stir well. Boil rapidly for a few minutes until reduced to about 4 tbsp.
Add the double cream and bring to the boil while stirring constantly. Taste and adjust the seasoning.