For the best texture, be sure to squeeze as much water as possible from the thawed spinach so the filling stays creamy instead of watery. The quiche can be made ahead, cooled completely, and refrigerated for up to 4 days or frozen tightly wrapped for up to 2 months. Reheat slices gently in a 350°F oven until warmed through to help keep the almond flour crust crisp. Feel free to switch up the cheese, using all Swiss, all cheddar, or another keto friendly melting cheese such as mozzarella or provolone while keeping net carbs low and fat content high.