How to Make It
Make the crust: Combine flour, salt, and sugar in a food processor and pulse to combine (or whisk together in a large bowl). Add butter and pulse until butter is about the size of peas. Add water, a little at a time, pulsing as you go, until dough looks crumbly but just starts to hold together when squeezed together in the palm of your hand, about 20 pulses. Transfer the crumbs to a sheet of plastic wrap and gather together, pressing gently to form a disk (use the plastic wrap to help). Refrigerate until firm, at least 2 hours and up to 4 days, or freeze up to 3 months.
Let dough sit at room temperature until it just gives when you press firmly with a thumb. On a lightly floured work surface, roll dough to a 12-inch circle. Transfer to a 9½-inch pie plate, pressing dough gently into the corners of the plate. Trim dough to a 1-inch overhang (sprinkle those strips with cinnamon-sugar and bake at 350°F until golden—you’re welcome!). Tuck overhang under and crimp as desired; freeze 15 minutes.
Preheat oven to 400°F with rack in the lower third. Line dough with a piece of parchment paper leaving a generous overhang, and fill with dried beans, rice, or pie weights. Bake on lower rack until edges are golden, 15–20 minutes. Let cool with beans or weights in place; remove when cool (bottom of dough will still look wet).
Make the custard: Reduce oven temperature to 350°. Place bacon in a large skillet over medium heat. Cook until crisp, flipping as needed, 5–7 minutes. Transfer to paper towels to drain. To bacon drippings add butter and onions and cook, stirring often until onions are tender and golden, 10–12 minutes, transfer to paper towels with bacon.
Whisk eggs, half and half, ½ teaspoon salt, several grinds pepper, and about ¾ of the cheese in a medium bowl. Pour egg mixture into par-baked crust. Scatter onions and bacon over top, breaking up the bacon as you are moved to, and sprinkle with remaining cheese. Place pie plate on a rimmed baking sheet and bake on lower rack until filling is set and slightly puffed, 40–45 minutes. Let cool at least 15 minutes before slicing.