In a food processor, combine the plain flour, icing sugar, fine sea salt, and lemon zest.
Add the diced unsalted butter to the mixture and pulse until it resembles breadcrumbs.
Incorporate the egg into the mixture and pulse until the dough starts to come together.
Divide the dough into two equal portions and shape each into a disc.
Wrap each disc in plastic wrap and refrigerate for at least 30 minutes before using.
