Grate 3 unwaxed lemons finely (just the yellow zest layer) then cut them in half and squeeze out the juice. Add the zest and the sieved juice to a bowl over a pan of hot water on the hob.
Weigh 8oz (200g) caster sugar and 4oz (100g) butter...
Add it to the juice/zest in the bowl, turn on the heat and cook slowly, stirring with a balloon whisk until the sugar is melted and doesn't feel 'gritty' any more...(about 5-10 minutes)Then add 2 beaten eggs to the mixture, whisking and mixing all the time (you do not want lemony scrambled eggs - so do not leave the kitchen at this stage!) I whisk it all the time at first, and then every minute or so...it takes about 20-30 minutes until it thickens up. (Don't overcook it as it thickens when it cools, too).
Pour into jars (sterilised in dishwasher or oven @ 160 degrees for 10 minutes.) Store in the fridge.