1) Heat the olive oil and half of the butter in a large skillet. Season the fillets with some salt and pepper. Place the fillets in the skillet and cook for about 5 minutes on each side.
2) When the fish is cooked, set it aside on a plate and deglaze the pan with the vermouth. Add the thyme and saffron, leaving it to bubble until it's reduced by two thirds. Add the remaining butter and whisk, then add the double cream and heat through.
Serve the fillets with the light saffron cream sauce and blanched asparagus.