Add the lemon juice, lemon zest, caster sugar, eggs and egg yolks to a pan or pot. Whisk everything together
Make sure you have your butter weighed out and ready (if your kitchen is warm, put it in the fridge to keep cold)
Place the pan on the hob/stove on a low heat
As the mixture heats, stir it gently but continuously. It will take around 5-8 minutes to thicken
To test that it's thick enough dip a wooden spoon into the mixture. Then run a line with your finger through the liquid on the spoon. If the line stays then you can take the pan off the heat. If the other liquid on the spoon drips into the line, you need to heat the mixture for longer
When it's ready, remove it from the heat and add the butter straight away, stir the mixture until the butter melts and combines
Pour the lemon curd into a bowl (you can sieve it at this stage if preferred or necessary) and cover with cling film so that the cling film directly touches the top of the curd, put it in the fridge to cool down fully
Store in an airtight container in the fridge for 1-2 weeks, or in the freezer for up to 3 months