Step 1

Preheat oven to 325 degrees F. Coat a 12-cup muffin tin with cooking spray.

Step 2

Heat oil in a large skillet over medium heat. Add potatoes, onion and 1/4 teaspoon salt and cook, stirring, until the potatoes are just cooked through, about 5 minutes. Remove from heat and let cool 5 minutes.

Step 3

Whisk eggs, cheese, milk, pepper and the remaining 1/2 teaspoon salt in a large bowl. Stir in spinach and the potato mixture. Divide the quiche mixture among the prepared muffin cups.

Step 4

Bake until firm to the touch, about 25 minutes. Let stand 5 minutes before removing from the tin.