Put the sugar, lemon juice, zest and butter in a pan on a low heat and stir with a wooden spoon until the sugar has dissolved and butter melted.
Turn the heat up to medium and whisk in the beaten egg and keep whisking until boiling.
Whisk for another minute (the mixture will thicken and coat the back of a wooden spoon). Thickens further on cooling.
Pour into hot sterilized jars and seal with lids immediately.
Allow to cool, then store in fridge and consume within 2 – 3 weeks.
Makes approximately 300 mls (1 to 2 small jars)!
Before you start, sterilise jars by washing in hot soapy water (or take straight from dishwasher). Fill with boiling water, empty and then place in oven for 20 minutes at 140°C where you leave them until the curd is ready. Washed metal lids should be sterilised with boiling water and then left to drain (if still wet place in oven once you’ve turned the heat off and run with just the fan for a few minutes to dry off).