To make the tart shell:
In a food processor place the flour, sugar, salt and butter. Pulse a few times until it resembles a coarse meal. Add the egg yolk and milk. Pulse until the mixture comes together into a ball. You can add a bit of cold water (1 Tbsp. at at time) if it is having difficulty coming together.
Take the ball of dough and flatten it out lightly on a lightly floured surface. Wrap it in plastic and place it in the refrigerator for about one hour or overnight.
Take dough and allow it to come to room temperature.
Preheat the oven to 350'F.
On a floured surface start rolling out the dough to make a 13" circle.
Place in a tart shell. Place a piece of parchment paper or foil on top of the shell. Fill with pie weights or beans.
Bake for about 20 minutes.
As soon as the shell comes out of the oven, brush with egg white.
To make the filling:
While the pastry is baking whisk together the eggs, sugar, orange juice, lemon juice, lemon zest and orange zest and cream until smooth.
Place the filling in the tart shell and bake for about 20-25 minutes.*
Allow it to cool before serving.
* Check with a toothpick after about 20 minutes so you don't over bake or see my notes on the "jiggle" test below.