For crust: Place the flours, sugar, orange zest, cardamom and salt in the bowl of a food processor. Pulse to combine. Scatter the cold butter over the dry ingredients. Pulse on and off until the dough is crumbly, with some smaller and larger pieces of butter.
Mix the egg yolk with 2 Tbsp. of water and with the motor running, drizzle through the feed hold. Add more water, if needed, and continue pulsing until the dough starts to come together into a ball. (The sound will change to a kind of grinding sound and then you'll know it's time to stop.)
Turn the dough out onto a piece of plastic wrap. Form into a ball, wrap well in plastic wrap and chill for about 2 hours or overnight.
For crust, filling and serving: Preheat oven to 425 degrees F. Press the chilled dough onto the bottom and up the sides of a 9" tart pan with removable bottom. (I used a 9" cake pan.)
Whisk the cornstarch with the salt. Add the eggs, maple syrup, brown sugar, vanilla, cream and milk. Whisk until smooth. Pour into the crust.
Bake for 10 minutes and lower heat to 350 degrees F. for an additional 25 minutes. The custard should be set and the crust will be lightly golden.
Transfer to a cooling rack and let cool completely before slicing. Can be served chilled or at room temperature.