Heat the oil in a strong-based frying pan then add the fillets and brown on both sides. Try to turn them over just once when they are browning. This helps to lock in their flavor.

Roughly chop the onion and serrano ham, peel the garlic cloves then add to the pan together with the sherry and thyme.

Cook over a medium heat stirring the mixture occasionally until the meat is done (approx 30 mins)