Place spring onion, tarragon and peppercorns into the Thermomix bowl and mill 10 sec/speed 8. Scrape down sides of bowl.
Add white wine vinegar and white wine, egg yolks and salt and cook 8 min/80°C/Butterfly/speed 4.
Add butter and whip 1 min/Butterfly/speed 4.
Scrape out of bowl immediately (or it may split) and serve with chopped chives on steak, seafood, prawns, waffles, eggs, pancakes, asparagus, mushrooms, grilled squash or zuchinni, as a dip for roasted potatoes...the list of deliciousness is endless.