Whisk together the sugar, passionfruit, eggs, egg yolks and zest in a small saucepan. Stir over low-medium heat until the sugar has dissolved.
Add the cold butter 3-4 pieces at a time, stirring until each addition is melted and incorporated.
Turn the heat to low and continue cooking the mixture for 2-3 minutes until it is thickened and coats the back of a spoon or leaves a thick coating on the side of the pan when you tilt it. (Test by drawing a line through the curd on the back of the spoon and the line should not drip)
Pour into sterilised conserve jars and store in the fridge.
This curd will keep for up to 3 weeks in the fridge, unopened. Once opened use within a week. It will also freeze well.
To sterilise the jars, boil them in a saucepan of boiling water for 10 minutes then set aside to drain, dry and cool. The second way is to wash the jars well with soapy water, rinse and then place them in an oven at 120C / 250F for 10 minutes. Let them cool.
You can swap the butter for a vegetable based spread if you would like to make this curd dairy free.
TOOLS USED IN THIS RECIPE
Use a good silicone spatula so as not to leave any behind
A heavy based saucepan is best to distribute heat more gradually and evenly