This sauce is good with stewed or boiled fish, with vegetables or with poached chicken.
5 free-range egg yolks
1 tsp English mustard powder
sea salt and pepper
5 tbsp lemon juice
6 tbsp extra virgin olive oil
120 ml (4 fl oz) double cream
Whisk the egg yolks in a bowl. Add the mustard powder, salt and pepper and lemon juice and put the bowl over a saucepan half full of simmering water.
Add the oil slowly while whisking constantly, and continue whisking until the sauce thickens. Be careful not to let it boil or the egg will curdle. Draw off the heat and beat in the cream. Return to the bain-marie and cook for a further couple of minutes.
Transfer the bowl to a basin of cold water and leave to cool.
preparation
The sauce can be prepared up to 1 day in advance and refrigerated. Remove from the fridge at least 2 hours before you use it to coat the tunny fish roll.