Potato-Crusted Ham Quiche

3 tablespoons olive oil
1 1⁄4 cups diced white or yellow onion (about 1 medium-size onion)
8 ounces white mushrooms, sliced
1 teaspoon salt
5 ounces baby spinach
1⁄2 cup diced cooked ham
2 medium-size russet potatoes (about 1 pound total)
1⁄2 teaspoon freshly ground black pepper
6 large eggs
1⁄2 cup milk
1⁄2 teaspoon Dijon mustard
1 cup shredded mild cheese (such as Fontina, Gruyère, or Swiss)

Preheat the oven to 450 degrees with one rack in the middle. Add 2 teaspoons of the oil to the skillet and heat over medium heat until the oil is hot, about 2 minutes. Add the onion, mushrooms, and 1/4 teaspoon of salt. Cook, stirring occasionally, until the onions are softened and the mushrooms are cooked through, about 10 minutes.

Add the spinach in two batches, cooking and stirring each time until the spinach wilts, about 30 seconds. The spinach will barely fit in the skillet at first, but will cook down quickly when stirred. Remove the skillet from the heat.

Drain off as much liquid as possible and scrape the vegetables into a large bowl. Add the ham and set aside. Wipe the skillet clean.

Use a paper towel to rub 1 teaspoon of the oil into the skillet. Using the coarse side of a box grater or a food processor, shred the potatoes. (You should have about 3 1/2 cups.) Squeeze the shreds in a clean kitchen towel until they’re as dry as you can manage. (The potato might discolor the towel. Remove the discoloration by immediately rinsing the towel under cold running water.)

In a medium-size bowl, toss the potatoes with the remaining 2 tablespoons oil, 1/2 teaspoon of the salt, and 1/4 teaspoon of the pepper. Press the potatoes into the skillet in an even layer across the bottom and all the way up the sides. Bake until the potatoes are golden brown at the edges, about 30 minutes.

Remove the skillet from the oven and set the oven temperature to 325 degrees. In a medium-size bowl, whisk together the eggs, milk, mustard, and the remaining 1/4 teaspoon each of salt and pepper. The ham and vegetables may have given off liquid as they sat. If so, drain it off. Distribute the cheese evenly atop the potato. Spread the ham and vegetables in an even layer over the cheese. Pour in the egg mixture.

Bake until the eggs are set at the edges (the center may still jiggle a bit), about 30 minutes. An instant-read thermometer should read 170 degrees in the center. Remove the skillet from the oven and transfer it to a rack to cool slightly, about 10 minutes. Serve warm or at room temperature. Leftovers can be refrigerated in a covered container for up to 2 days.
Excerpted from Will it Skillet by Daniel Shumski (Workman Publishing). Copyright © 2017.