Mix the lemon juice and caster sugar together in a large microwave safe jug or bowl (I use my Pampered Chef batter bowl here which is a heavy duty large glass jug which is safe in the oven as well as the microwave so do check if yours is before you make this).

Stir in the butter.

Whisk the eggs very well until combined and pass through a fine sieve into the jug of lemon juice etc. Discard any stringy bits in the sieve then wash and dry it thoroughly as we'll need it again later.

Stir well then place in the microwave for 60 seconds on high. Take the jug/bowl out and whisk it well - it's unusual to see any change after the first zap.

Return to the microwave and give it three more 60 seconds on high, followed every time by taking it out of the microwave and whisking it throughly - it should be thickening with every zap, initially around the edges. I find after 4 minutes, it just needs another 30 seond pulse before it's thickened enough to set on cooling (it will be like thick double/heavy cream when it's ready), so do feel free to go with lower increments of time as you approach the end of cooking if you think it's almost there.

Pass the curd through the clean and dry sieve to catch any tiny bits of overcooked egg (I've found you barely get a single grain with this method but feel happier giving it a second sieve to ensure smoothness) into sterilised* jars and once cooled to room temperature, store in the fridge.

I've found it lasts up to 2 weeks in the fridge, if you don't eat it all!