1) Add flour and salt for crust to a bowl and then cut in the butter using fingers or a fork until it’s in small pea-sized pieces.
2) Add enough cold water to the dough to bring it together in a bowl. That’s probably 6-8 tablespoons of ice cold water.
3) Split the dough into two balls and wrap them in plastic wrap. Refrigerate them for 30 minutes at least.
4) Once the dough is chilled, lightly flour a clean surface and roll out each dough ball to two inches in diameter larger than your pan. If it tears a bit, that’s okay. Just work slowly and patch up the crust as you go.
5) Carefully transfer the dough to your pie pan. Press the dough carefully down into the corners of the pan and, if you want, do something decorative with the edges.
6) Add a circle of parchment paper to the bottom of you pie and fill it with uncooked dry beans (or pie weights). Poke holes around the edges to help steam escape.
7) Prebake this at 425 for 10-12 minutes until it’s lightly browned.
8) For filling, heat butter in large pan over medium heat and add all your onions. Cook until they start to brown slightly, about 20 minutes.
9) In a separate bowl, whisk together all your other ingredient. Let your onions cool and then stir them in to the mix.
10) Pour this into your pre-baked crust, grate some cheese on top and bake it for 40 minutes at 325 until it’s golden brown and the center is firm.