For the chateaubriand sauce: melt 25g of the butter in a pan and add the shallots. Fry gently until golden brown. Add the mushrooms and garlic and cook until you can smell the garlic.
Pour in the wine and reduce for 2 minutes. Add the chicken stock and reduce by half. Whisk in the remaining butter and keep the sauce warm. Just before serving, add the tarragon leaves and check the seasoning.
For the chunky chips: heat the goose fat over a medium heat in a large deep frying pan. Add the potatoes and cook until tender. Remove with a slotted spoon and drain on kitchen paper. Save the beef fat fro crisping the chips later.
For the beef: light the barbecue or preheat the grill. Season the beef and cook on the hot barbecue or under the grill for up to 20 minutes on each side, or until cooked to your liking. Leave to rest while you finish the chips.
Return the pan of goose fat to a high heat. Add the potatoes and cook until crisp and golden. Drain on kitchen paper.
Serve the cote de boeuf with the chips and chateaubriand sauce.
Notes & Tips
Recipe reproduced with permission of Good Food Channel.