Measure flours, corn starch, sugar, and xanthan gum into the bowl of your food processor, blitz to combine. Add cream cheese, butter, lemon zest and egg, blitz a few times until mixture resembles gravel.
Stream in cold water as you run the food processor, just long enough to start to bring it together as a dough – you may need to use a little more or less water. Do NOT over-process it!
Remove dough from processor, knead lightly to bring it together as a ball. Wrap in plastic film, chill for 1 hour.
Preheat oven to 450 F (230 C), lightly dust your work surface with extra corn starch. Roll your crust out to about ¼″ thick.
Line a pie pan with the crust, trim the edges of the crust to only slightly longer than the edge of the pie plate. Use your fingers to crimp/ruffle the edge of the pie.
Use a fork to prick some holes on the bottom of the crust. Chill in fridge for 15 minutes. Once chilled, bake pie crust for 10-12 minutes, or until golden brown. Remove from oven, allow to cool to room temperature while you prepare the filling.