1. In the bowl of the food processor (or with an Immersion Blender), mix the butter and sugar for about 2 minutes, or until completely smooth.
Slowly add the eggs and mix for just 1 minute. Add the lemon juice and mix to combine. The mixture will look curdled, but it will smooth out as it cooks.
2. Divide mixture into Mason jars and place the lids, turning until the lid catches, but not super tight. Place 1.5 cups of water in the Pressure Cooker and place a trivet inside. Place Mason jars on top of trivet.
Lock on lid and close the Pressure Valve. Cook on high heat for 10 minutes. When cook time is up allow a Natural Pressure Release. Remove jars from Pressure Cooker and carefully open.
3. Add in the Lemon Zest and stir into the curd, until very smooth. Place lids on Curd and tighten just until the lid catches. Allow to cool for 25 minutes and then place in the refrigerator overnight. Curd will thicken as it cools.
Curd will keep in the refrigerator for a week or in the freezer for 2 months. This recipe can easily be doubled. You can also use one large vessel, instead of mason jars. Place foil tightly over the top.
Overmixing the eggs will cause the Curd to overflow and seep out of the Mason Jars.
Cook's notes: If you don't have a pressure cooker you can make this on your stove-top, however it is more manageable in smaller batches using this method. Simply crack eggs into a stainless steel bowl, add sugar, lemon juice & zest and whisk together. Transfer over a bain marie (or double-boiler) and whisk continuously until thick and holds a ribbon. Stir in the butter, chill and seperate in to jars.