In a glass or ceramic bowl, whisk together the eggs and yolks, white sugar, lemon zest, lemon juice and salt. For an extra smooth finished curd, blend the mixture with a stick blender.
Cover the bowl tightly in foil, to prevent any moisture while cooking.
Pour 1 cup (250ml) of cold water into the inner pot, then place the trivet inside and carefully place the tightly wrapped curd on the trivet.
Secure the lid and select Pressure Cook and set the time to 3 minutes.
When the cooking program finishes, allow the pressure to release naturally for 2 minutes, then quick release any remaining pressure.
Remove the bowl from the Instant Pot and check the curd mixture, it should be a thick custard consistency. Should the curd not be at this stage, simply microwave the mixture for 30 seconds.
Whisk in the butter, then pass the curd through a sieve to remove any bits. Divide the curd between sterilized or very clean glass jars, and pop them in the fridge. The curd will last in the fridge for 1 ½-2 weeks