First make a seasoning stock: Peel and chop the shallot. Bring to the boil with peppercorns, vinegar and 6 tablespoons of water. Let it boil down to about half of its original volume, sieve and let it cool down. Melt butter.
Whisk the egg yolk with the seasoning in a hot water bath with the whisk of the mixer until thick and creamy (the bottom of the bowl must not get too hot, otherwise the egg yolk will stagnate!) Whip the butter first drop by drop, then in a thin stream under the egg mass, so that a creamy sauce is formed.
If the hollandaise sauce becomes too firm, stir in some cold water. Season to taste with salt, cayenne pepper and lemon juice, then wash and chop the tarragon and chervil and stir into the hollandaise.