Lemon Curd

Steps

1. 1
   Finely grate the zest of the lemons, avoiding the bitter white pith, then squeeze them: you need about 150 ml of juice.
2. 2
   Whisk the eggs and egg yolk with the sugar in a heatproof bowl until smooth, then whisk in the lemon juice and zest and add the butter.
3. 3
   Set the bowl over a pan of barely simmering water, its base clear of the water, and stir constantly with a spatula for 10–15 minutes as the butter melts and the curd thickens.
4. 4
   It is done at about 80°C, when it coats the back of a spoon thickly and a finger drawn through leaves a clean line. Never let it boil, or the eggs scramble.
5. 5
   Pass it through a fine sieve for a silky curd, then pour it into hot sterilised jars.
6. 6
   Lay a disc of baking paper on the surface, seal and leave to cool, then refrigerate. It sets further as it chills and keeps for two weeks.