How to Make It
Preheat oven to 375°F. Spray 8 cups of a 12-cup muffin pan with cooking spray. Using a mandoline, slice potato lengthwise into 1/16-inch-thick slices. Layer potato slices evenly on bottom and along sides of prepared 8 muffin cups, spraying with cooking spray between each layer. Bake until softened and lightly browned, about 13 minutes.
Meanwhile, heat oil in a large nonstick skillet over medium. Add leek, and cook, stirring occasionally, until softened but not browned, about 4 minutes. Add asparagus, cover, and cook, stirring occasionally, until softened, about 3 minutes. Add thyme, and cook until fragrant and asparagus is tender, about 1 minute. Remove from heat. Let cool slightly. Distribute vegetables evenly among potato crusts.
Whisk together cheese, milk, eggs, salt, and pepper in a medium bowl. Pour about 1/4 cup egg mixture over vegetables in each crust. Bake until set and potatoes are golden, about 13 minutes. Let cool 3 minutes. Run a knife around edges, and gently lift out of muffin pan. Sprinkle with chives.