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 a little olive oil and heat until transparent. Add the tarragon stalks and the 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. Add a squeeze of lemon juice.
Heat a frying pan and add a little oil. Sear the steak on both sides and continue cooking to your required degree of cooking.
Preheat the oven to 180'c
Parboil the potatoes in salted water for 6 minutes. Allow to cool and then cut into thick slices.
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. When nicely coloured add the butter to the pan and transfer the potatoes to the oven for 5 miutes to finish cooking.
Dress the rocket leaves with balsamic vinegar and olive oil.
Serve the potatoes alongside the steak, add a handful of dressed rocket leaves and finish with the bernaise sauce. Serve immediately.
«Use your favourite cut of beef in this simple and delicious recipe.»