• Preheat oven to 425°F.

Optional Hash Browns Crust

• Combine the thawed hash browns with the melted butter, salt and pepper.

  Press the hash browns into an 8 or 9-inch pie plate, making sure to work them up the sides of the dish.

Asparagus Gruyere Quiche

• Toss the leeks and asparagus with olive oil and arrange on a baking sheet lined with parchment paper. Slide into the oven, along with the hash browns-lined-pie plate (or other crust-lined pie plate), and bake for 20 minutes.

  Lower the oven temperature to 350˚F.
• Whisk the 4 large eggs, half-and-half, milk, mustard powder, salt, and pepper in a large bowl.
• Separate 2 additional eggs, and save the yolks for another use.

  Whip up the egg whites using a hand mixer, or whisk, until they have soft peaks. When you turn the mixer or whisk upside down, they should droop, but not fall back into the bowl.
• Fold the whipped egg whites into the egg and milk mixture using a rubber spatula, and fold in the grated cheese.

  Pro tip: I find it much easier to fold egg whites into a mixture when I add them only ⅓ at a time, whether it's this quiche or a cake. See the Preparation Tips in the post for more details.
• Arrange the asparagus and leeks evenly in the pie plate. Pour the egg mixture over the top. Sprinkle with nutmeg, and bake for 25 minutes, or until a knife inserted into the middle of the quiche comes out clean.

  High altitude tip: When baking this at high altitudes add 5 - 10 minutes to the bake time.
• Cool on a cooling rack for at least 15 minutes before slicing into wedges, or cool to room temperature.