How to Make It
Combine the flour, sugar, and salt in a stand mixer fitted with the paddle attachment; beat on low speed until combined. Add butter, and beat until mixture resembles a coarse meal with a few pieces of butter visible, 2 to 3 minutes. With the mixer running, drizzle in 6 to 7 tablespoons ice water, beating until dough is still crumbly but just holds together when squeezed.
Turn dough out onto a clean work surface. Knead 1 to 2 times, pressing to incorporate any shaggy pieces. Press into a 6-inch wide disk. Wrap with plastic wrap, and chill at least 1 hour.
Place rack in lowest position of oven; preheat to 375°F. On a floured work surface, roll out dough to an 14-inch round; ease it into a 9-inch glass or ceramic pie plate. Trim the overhanging dough to 1 inch and fold it under itself. Crimp decoratively, dock the bottom of the dough, and chill the crust until firm, about 30 minutes.
Line the crust with parchment paper, leaving some overhang, and fill with pie weights or dried beans. Bake in preheated oven until the crust is dry around the edges and just beginning to brown, 25 to 35 minutes. Carefully remove parchment and weights, and reduce oven temperature to 350°F. Bake at 350°F until crust is set and beginning to brown in the center, 15 to 20 minutes. Let the crust cool completely before assembling the quiche.
Cook the bacon, onion, butter, thyme, and bay leaf in a medium saucepan over medium-high, stirring occasionally, about 5 minutes. Reduce heat to low (mixture should still slowly bubble) and cook, stirring occasionally, until bacon and onions are very soft, about 20 minutes. Remove from heat, and let cool. Remove and discard thyme and bay leaf. Using a slotted spoon, transfer cooked bacon and onion to a plate to cool, leaving oil in pan.
Place rack in the middle of the oven; preheat to 350°F. Purée eggs in a blender on medium-high speed until foamy, about 30 seconds. Add the half-and-half, salt, cayenne, and nutmeg. Purée on medium-low speed until custard is smooth, about 15 seconds.
Set the baked pie crust in the pie plate on a large rimmed baking sheet. Sprinkle the cheddar evenly over the bottom of the crust. Top with bacon-onion mixture. Pour half of the custard into crust. Transfer quiche to oven, then carefully pour remaining custard into crust. Bake quiche in preheated oven until edges are set but center slightly wobbles, 45 minutes to 1 hour. Let cool before slicing. Serve warm or at room temperature.