zest and juice of 4 lemons
3 eggs and 1 egg yolk
Put the lemon zest and juice, the sugar and butter (cut into cubes) into either a double boiler or a saucepan on top of a larger saucepan full of simmering water.
Stir with a whisk occasionally until the butter has melted.
Beat the eggs and egg yolk lightly, then stir into the lemon mixture. Let the curd cook, stirring regularly, for about 10 minutes, until it’s thick and custard-like. It should feel heavy on the whisk.
Remove from the heat and stir occasionally as it cools. Pour into spotlessly clean jars and seal. It will keep for a couple of weeks in the fridge. Eat as a spread on toast or use in desserts.