Method:
Step 1
Preheat the oven to 475°F. Allow the chateau briand to come to room temperature then rub all over with the olive oil and sprinkle with sea salt and black pepper.
Step 2
Heat a heavy-based oven proof frying pan. Seal the chateau briand over a high heat for about 6 minutes until golden brown on all sides, turning regularly.
Step 3
Transfer the pan to the oven and roast the steak for about 12 minutes for medium-rare, or to your liking. Remove from the oven and allow to rest in a warm place for 10 minutes.
Step 4
Meanwhile, prepare the Béarnaisesauce. Melt the butter in a small pan or in the microwave.
Step 5
Combine the white wine, vinegar, one table spoon of the tarragon, the shallot and white pepper in a pan. Bring to a simmer and reduce until about one tablespoon of liquid remains.
Step 6
Strain in to a liquidizer or miniblender, pushing down the tarragon leaves to extract the liquid.
Step 7
Add one tablespoon of warm water to the liquidizer together with the egg yolks and turn on the machine. Pour the hot butter into a jug and start to pour the butter very slowly on to the egg yolks. As the sauce emulsifies, increase the butter flow to a thin, steady stream.
Step 8
As the Béarnaise sauce thickens, you will notice a change in the sound of the machine. If the sauce is too thick, add a little more warm water or lemon juice to taste.
Step 9
Add the remaining tarragon leaves, the parsley and cayenne pepper and blend briefly. Season with salt. Keep the sauce warm until you need it in a bowl or jug set in a pan of hot but not boiling water.
Step 10
Carve the chateaubriand into 12-16 slices, divide between warmed plates, garnish with watercress and serve with Béarnaise sauce on the side and a big bowl of chips.