2 tablespoons butter, softened, plus more for pan
4 medium russet potatoes (about 2 pounds), peeled
1 1/2 teaspoons kosher salt, divided
3/4 teaspoon freshly ground black pepper, divided
2 tablespoons vegetable oil
3 tablespoons unsalted butter, divided
4 medium shallots, thinly sliced
6 large eggs, room temperature
1 1/4 cups half-and-half or light cream
1 tablespoon Dijon mustard
Pinch of grated nutmeg
6 ounces Fontina cheese or Emmenthal cheese, grated (about 1 1/2 cups)
1/2 bunch asparagus (about 1/2 pound), ends trimmed
Preheat oven to 375 degrees. Brush a 9-by-2 1/2-inch springform pan with butter. Line the sides of the pan with strips of waxed paper (the same height as pan); brush paper with butter.
Using the coarse grater disk on a food processor or the largest holes on a box grater, shred potatoes. Toss with 1 tsp. salt and 1/2 tsp. pepper in a large bowl. Transfer to a clean dishtowel, gather together ends of towel, and thoroughly wring out excess liquid; Transfer potatoes to a bowl and add butter, 1 egg, salt, and 1/4 teaspoon pepper.Pat into bottom and up sides of prepared pan. Place on a rimmed baking sheet; bake until set, 15 to 20 minutes.
Meanwhile, melt remaining 1 Tbsp. butter in a small skillet over medium heat. Add shallots and sauté until translucent, 5-6 minutes; set aside.
Whisk eggs, half-and-half, mustard powder, nutmeg, remaining 1/2 teaspoon salt, and remaining 1/4 teaspoon pepper in another large bowl and set aside.
Sprinkle Fontina or Emmenthal cheese, and sautéed shallots evenly over bottom of crust, then pour in egg mixture. Arrange asparagus decoratively on top. Bake until quiche is set and crust is well browned, 30-35 minutes. Let cool to room temperature before cutting into wedges.