175g caster sugar
2 tsp. cornflour
2 lemons, juiced
2 limes, juice and zest
Whisk eggs, sugar and cornflour. Add citrus.
Progressively whisk over a moderate heat for 5-8 minutes until it has thickened.
Add butter at end.
Pour into sterilised jars, seal and place in the fridge.
Keeps up to 3 months.