Place the butter in a pan and clarify - melt slowly, allowing the fat to separate from the water and milk solids. Skim off the foam that rises to the top.
Pick the leaves from the tarragon and parsley. Chop the leaves making sure not to bruise the tarragon. Reserve the tarragon stalks.
Peel and finely dice the shallot. Place in a pan with the tarragon stalks, dry white wine and vinegar. Allow to reduce to a fifth of the original volume then remove from the heat and pass through a fine sieve.
In a bowl over a pan of simmering water, whisk the egg yolks with the reduction of wine and vinegar. Whisk until you have a thick sabayon. Remove from the heat and slowly whisk in the melted butter until you achieve a mixture with the consistency of mayonnaise. Add the chopped herbs and season with salt and pepper. Finish with a squeeze of lemon juice.
Preheat the oven to 180'C.
Parboil the potatoes in salted water for 6 minutes. Allow to cool and then cut into thick slices.
Pick the leaves from the parsley and slice finely.
Heat the oil in a frying pan and add the potatoes when the oil is hot. Season with salt and pepper and cook until golden brown.
Finish with the chopped parsley.
Heat a griddle pan until very hot. Season the steaks on both sides with salt and pepper and drizzle on the sunflower oil. Grill the steak on both sides and continue cooking to your required degree of cooking. Allow to rest for a few minutes before serving.
Serve the potatoes alongside the steak, add a large sprig of watercress and finish with the bearnaise sauce. Serve immediately.
«This is a classic recipe for Bearnaise sauce, play around with the flavours by adding different soft herbs such as chives or basil tailored to the garnish for the steak.»