Chateaubriand with mustard Béarnaise and shoe string chips

Method

1. Preheat the oven to 180C/gas 4 and a deep-fat fryer.

2. Pour a little oil in a griddle pan and bring it up to smoking temperature. Put the steak whole in the pan and allow it to sizzle. Turn and sear on the other side. Holding the steak with tongs, brown the edges all the way around. Put it in the oven to finish cooking - this will take about 20 minutes for medium-rare.

3. For the béarnaise sauce: put the shallot, black peppercorns, white wine vinegar, white wine and a little of the tarragon in a small pan and reduce until about a quarter of the volume remains. Pick out the peppercorns.

4. Put the egg yolks in a bowl with the vinegar reduction. Whisk until the sauce begins to emulsify. Add the hot melted butter a drop at a time, whisking between each addition. The sauce will start to thicken. If it splits, add a drop of hot water. Once all the butter is added, stir in the mustards, the rest of the chopped tarragon and season.

5. For the chips: fry the potato chips in a deep-fat fryer until golden. Drain well and keep in a warm oven to maintain the crispness until ready to use.

6. Cut in the steak in half and arrange on 2 plates with a dollop of béarnaise and a handful of watercress.