Makes: 2 generous portions
Preparation time: 20 minutes
• 1 small onion, finely chopped
• 45ml white wine or tarragon vinegar
• 5 black peppercorns
• 4-5 sprigs tarragon
• 2 egg yolks
• 5ml Dijon mustard
• 150g soft butter, cut into blocks
1 Place the onion, vinegar, peppercorns and tarragon in a small saucepan. Bring to the boil and simmer until the liquid reduces to about 20ml.
2 Place the egg yolks and mustard in a glass bowl that fits the top of a pot. Pour boiling water about 2cm deep in the pot and make sure the bowl doesn’t touch it. Whisk the egg mixture constantly over simmering water until it thickens, then add the vinegar (use a wooden spoon or the saucepan lid to hold back the onion, peppercorns and tarragon) and beat again until thick.
3 Add a small block of butter at a time while whisking constantly. The sauce will thicken and take on a velvety texture but be careful not to overheat it as it may curdle – keep the water on a slow simmer. Season the sauce with a little salt and keep it warm over hot water (you can turn the plate off) while you grill the meat.
TIP If the sauce curdles, you can try to save it by removing the glass bowl from the heat and dipping it in a sink of cold water before beating in a tablespoon of boiling water – keep beating it for as long as you can. Otherwise, start over with two new egg yolks and whisk the curdled sauce bit by bit over a low heat.