Spinach Feta Quiche with Flakey Phyllo Dough Crust

tablespoon extra-virgin olive oil

leeks, white and light green parts only (about 1 small leek)

cups fresh baby spinach

large eggs

large egg whites

non-fat milk

plain non-fat Greek yogurt

 teaspoon kosher salt

black pepper

 cup (4 ounces) crumbled reduced fat feta cheese

unsalted butter, melted

 sheets, thawed, cut to be 12 inches on one side (the other side may be shorter depending upon the brand you purchase)