In this quiche recipe, I wilt the spinach over medium heat before adding it. Other quiche recipes put in chopped spinach but don’t wilt it first. It depends on your personal preference and how much spinach you’re adding. Generally, veggies that release a lot of liquid when they cook SHOULD be pre-cooked so that they won’t make your quiche watery (mushrooms, for example). Spinach doesn’t release much liquid, so the choice is yours.