Boil the vinegar together with peppercorns and tarragon, reduce by half. Strain and reserve (see Secrets for success on storing, below).
Boil a large pan of water, then reduce to a simmer. Using a large balloon whisk, beat together the yolks and 2 tsp of the reduced wine vinegar in a heatproof bowl that fits snugly over the pan.
Beat vigorously until the mixture forms a foam, but make sure that it doesn’t get too hot. To prevent the sauce from overheating, take it on and off the heat while you whisk, scraping around the sides with a plastic spatula. The aim is to achieve a golden, airy foam (called a sabayon), which forms ribbons when the whisk is lifted.
Whisk in a small ladle of the warmed butter, a little at a time, then return the bowl over a gentle heat to cook a little more. Remove from the heat again and whisk in another ladle of butter. Repeat until all the butter is incorporated and you have a texture as thick as mayonnaise. Finally, whisk in lemon juice, salt and pepper to taste plus a little warm water from the pan if the mixture is too thick.
If the sauce mixture starts to ‘split’ or curdle, immediately scrape the mixture into a clean bowl and whisk in 1 tbsp ice-cold water, then continue whisking in the remaining butter just a ladleful at a time.
Salt breaks down the yolks if you add it too early, so season your sauce at the end.
Melting the butter
Heat a 250g pack chopped butter in a shallow pan. As it foams, scoop off the froth and scum using a small ladle or large metal spoon. Don’t use a slotted spoon or the scum will slip back into the butter. (Don’t waste the froth – it can be used in potatoes or for dressing hot vegetables). You should have around 200ml of warmed butter for the sauce. You can melt the butter in a microwave, but keep it covered as it melts or it will spit. Leave to cool a little before adding to the eggs.
Storing reduced wine vinegar
When vinegar has reduced, strain back into the bottle, cool and store as usual.
Olive oil hollandaise
Use 200ml of medium flavour olive oil (not extra virgin oil) instead of the butter, and heat until warm. Perfect with roasted vegetables and grilled fish.