In a bowl of a stand mixer fitted with a paddle attachment, mix together the flour and salt until combined. Add the butter and mix on medium speed until you get hazelnut size pieces of butter in the flour. Add just enough water until the dough comes together when pressed. Wrap and refrigerate for 40 minutes until firm.

Preheat the oven to 375F. On a lightly floured surface, roll the dough out into a circle, approximately 12 inches in diameter. Lay a sheet of parchment on top and top with baking beans. Blind bake for 15 minutes and remove the beans and parchment. Bake again for 15-20 minutes until lightly golden brown. Set aside to cool.

Bring a saucepan of water(about 4 inches) to a simmer, add the onions and let it simmer for 3-4 minutes until just soft but it still retains its shape. Drain well.

In a bowl, whisk together the eggs until thoroughly combined. Add the rest of the ingredients and mix to combine.

Pour the filling to the pie crust and bake for 35 minutes until just set and the top is golden brown. Let cool before slicing and serving.