1
Preheat the oven to 350 degrees Fahrenheit.
2
Slice 2 medium sweet potatoes very thin using a knife, mandoline, grater, or food processor.
3
In a bowl, mix the sweet potato slices with 1 tablespoon of olive oil using a spoon or spatula.
4
Oil a 9-inch pie plate or spray it with cooking spray.
5
Arrange the sweet potato slices in concentric circles to cover the bottom of the pie plate, overlapping them.
6
Cut round slices of sweet potatoes into halves or thirds and place them along the edges of the pie plate, overlapping with the flat side down.
7
Bake the sweet potato crust in the oven at 350 degrees Fahrenheit for 20 minutes until the potatoes are tender.
8
In a hot pan over medium-high heat, add 1 tablespoon of olive oil and let it heat.
9
Add 0.5 cup of sliced or chopped onions and sauté for 3 minutes until softened.
10
Add 3 cloves of minced garlic and sauté for a minute.
11
Add 3 crimini mushrooms and sauté until they become tender and browned.
12
Add 5 ounces of fresh spinach (about 2 cups) and sauté for 3 minutes until soft, then turn off the heat and let it cool.
13
After 20 minutes, remove the crust from the oven and let it cool on a wire rack while raising the oven temperature to 375 degrees Fahrenheit.
14
In a bowl, whisk together 4 large eggs and 1/3 cup of egg whites.
15
Add 0.5 cup of milk, 0.25 teaspoon of salt, 0.25 teaspoon of black pepper, and 0.25 teaspoon of crushed red pepper (optional) to the egg mixture and whisk until combined.
16
Layer the sautéed spinach and mushroom mixture in the baked sweet potato crust.
17
Slowly pour the egg mixture over the spinach and mushrooms in the crust.
18
Add feta cheese on top of the egg mixture (amount not specified).
19
Place the quiche on a sheet pan and bake in the oven at 375 degrees Fahrenheit for 30 to 35 minutes until the egg is set.
20
Let the quiche cool for about 10 minutes before slicing.
