Flan Patissier (French Custard Pie)

Step 1
For the pastry, combine flour, butter, potato starch, sugar, and salt in the bowl of a food processor and process until it has the consistency of sand.

Step 2
Combine milk and egg yolk in a small bowl. Add to the flour mixture and mix by hand until the mixture is evenly moistened. Do not overwork the pastry. Wrap pastry dough in plastic wrap and refrigerate for at least 30 minutes.

Step 3
Grease and flour a 9-inch springform pan.

Step 4
For the filling, combine milk, 1/2 of the sugar and split and scraped vanilla bean in a large, heavy saucepan over medium heat. Bring to a boil, stirring occasionally, until sugar has dissolved. Remove from heat once milk boils.

Step 5
While the milk is heating, whisk eggs and remaining sugar in a large bowl until well combined. Stir in cream and cornstarch, and whisk until well blended.

Step 6
Whisk egg mixture into the cooled milk, stirring constantly.

Step 7
Return everything back into the saucepan and bring to the boil over medium heat, whisking constantly to prevent eggs from setting. As soon as custard begins to thicken, remove from heat and whisk constantly for a few minutes while it cools.

Step 8
Preheat the oven to 400 degrees F (200 degrees C).

Step 9
Remove pastry from the refrigerator. Roll out pastry on a lightly floured surface into a circle large enough to cover the bottom and sides of the springform pan. Line a springform pan and sides with the pastry and pierce several times with a fork. Store in the refrigerator until filling is cooled down enough.

Step 10
Briefly beat cooled pastry cream with an electric mixer to smooth it out. Pour into the pastry shell and even out the surface with a spatula.

Step 11
Bake in the preheated oven for 20 minutes. Increase temperature to 470 degrees F (240 degrees C) for an additional 10 minutes to brown the surface, making sure the custard does not burn. To speed up browning the top you can also place on a rack closer to the top.

Step 12
Remove pie from the oven and allow to cool to room temperature. Refrigerate cooled custard pie for 4 hours before serving.

Step 13
To unmold, run the blade of a knife along the inside of the mold, to loosen the flan. Then carefully remove the ring off from the springform pan.