Preheat your oven to 375℉.

Make the pie dough – In a bowl, combine the flour and salt. Then add the cubed butter and work into the flour until you have coarse pieces. Then add in the water and mix together until a dough forms. Wrap in plastic wrap and set in the fridge for at least 2 hours or overnight.

Cook the fix-ins – On medium heat in a skillet, cook the sliced bacon until crispy, about 10 minutes. Remove it and put it on a paper towel lined plate. To the same skillet (without removing the bacon fat) add the onions. Sauté for about 3-5 minutes until it's softened, then add the spinach and cook for an additional 3 minutes until wilted. Set aside.

Roll out your pie dough – On a lightly floured surface, roll out the dough to about ¼" thick and make sure it covers the circumference of the pie dish and then some (you'll want overhang). Carefully layer it into the pie dish and fold the hangover edges under until it's just at the edge of the dish. Crimp the edges using your pointer finger and thumb on one hand, and just your thumb on the other.

Blind bake your dough – Layer parchment paper down hanging out of the pie crust and add pie weights or dry beans. Bake for 15 minutes, then remove the pie weights/beans, prick the bottom of the crust all over with a fork, then bake for 5 more minutes. Reduce the heat to 350℉ once you've removed it. 

Mix the filling – Whisk together the eggs, whole milk, and heavy cream. Add in the bacon, onions, spinach, and grated cheese. Sprinkle with ½ teaspoon salt and ¼ teaspoon pepper. Pour the filling into the crust (it's ok if it's hot still).

Bake – Place the quiche on a baking sheet, and bake for 45-55 minutes. Let it sit for about 15 minutes before cutting into it.