To make the pastry, combine the butter, icing sugar, flour and lemon zest in the bowl of a food processor.
Pulse until the mixture resembles rough bread crumbs.
Add the egg yolks and with the blender running, pour in the water, spoon by spoon until the mixture comes together in a ball.
Turn the mixture out onto a floured surface and shape into 2 discs. Wrap in plastic wrap and place in the fridge for 15 minutes.
Pre-heat the oven to 180°c. Roll the chilled pastry out on a floured surface and press into 2x 28cm tart cases.