French Custard Pie

To create a pastry, combine flour, butter, potato starch, sugar, and salt in the bowl of a food processor and process until it reaches a coarse, granular texture. Combine milk and egg yolk in a small bowl, then add to the flour mixture and mix by hand until the dough is evenly moistened. Avoid overworking the pastry, as this can lead to a tough final product. Wrap the dough in plastic wrap and refrigerate for at least 30 minutes to allow it to firm up.

Next, prepare the springform pan by greasing and flouring a 9-inch round cake pan. This will ensure that the pastry releases easily once it's baked.

For the filling, combine milk, 1/2 of the sugar and a split and scraped vanilla bean in a large saucepan over medium heat. Bring to a boil, stirring occasionally, until the sugar has dissolved completely. While the milk is heating up, whisk eggs and remaining sugar in a separate large bowl until well combined. Stir in cream and cornstarch, then whisk until smooth.

Once the milk has boiled, whisk the egg mixture into it, stirring constantly to prevent the eggs from setting. Return everything back into the saucepan and bring to a boil over medium heat, whisking constantly to achieve a smooth consistency. As soon as the custard begins to thicken, remove it from heat and whisk constantly for a few minutes while it cools down.

Preheat the oven to 400 degrees F (200 degrees C). Remove the pastry from the refrigerator and roll it out on a lightly floured surface into a circle large enough to cover the bottom and sides of the springform pan. Line the pan with the pastry, leaving some excess around the edges. Pierce several times with a fork to prevent the pastry from bubbling up during baking.

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

Bake in the preheated oven for 20 minutes. Increase the temperature to 470 degrees F (240 degrees C) for an additional 10 minutes, or until the surface is golden brown. To speed up browning, you can also place the pie on a rack closer to the top of the oven.

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

To unmold, run the blade of a knife along the inside of the mold to loosen the flan. Then carefully remove the ring from the springform pan, taking care not to spill any of the creamy filling.