Ingredients

• 100 g butter
• 1 finely chopped medium red onion
• 2 tbsp lemon juice
• 1 tbsp white wine vinegar
• 1 dl white wine
• 2 tbsp estragon
• 400 ml whipping cream
• 2 beaten egg yokes
• salt
• freshly ground pepper
• thermometer

Instructions

1. Melt the butter at a medium heat in a saucepan
2. Add the finely chopped onion
3. Let the onion turn glassy (about 5 minutes at medium heat), make sure the butter doesn't burn (goes brown)
4. Add the white wine and then turn up the heat till the sauce bubbles to cook off the alcohol, leave to bubble for 2 minutes
5. Turn the heat down and add the estragon, lemon juice and white wine vinegar
6. Pour in the cream, stir and monitor the temperature with the thermometer
7. Once the temperature is around 70°C, keep it there and then add the two beaten egg yolks
8. Stir the mixture and add salt and pepper to taste
9. Let the mixture simmer for another 5 minutes or so and then strain the sauce through a fine sieve and serve within 30 minutes