Makethe crust: In a large bowl whisk together flour and salt until combined. Using your hands, add butter, working it into the flour until the mixture resembles pea-size crumbs. Add ice water by the tablespoon until the mixture forms into a crust. Form into a disc, wrap in plastic wrap, and refrigerate until firm, 30minutes.
Preheat oven to 375°F. On a lightly floured surface, roll out crust until ¼” thick.Loosely drape over a 9” pie plate and crimp edges. Refrigerate until ready to use.
Ina large skillet over medium heat, cook bacon until crispy, 8 minutes. Transfer to a paper towel-lined plate to drain.
Scatter cooked bacon on pie crust with 1 cup Gruyere and shallot. In a large bowl,whisk together eggs, cream, cayenne, and nutmeg and season with salt. Pour mixture over bacon and cheese. Sprinkle with remaining 1/2 cup cheese.
Bake until crust is golden and eggs cooked through, 40 minutes. Let cool 15minutesbefore slicing and serving.