The best way to reheat egg casseroles is to set one serving at a time in an air fryer preheated to 350°F. Cook for about 4 minutes, which allows enough time for the the eggs to warm and the crust to crisp up again. (another reason I love my u003ca href=u0022https://cookathomemom.com/air-fryer-cook-times-chart/u0022u003eair fryer!u003c/au003e). If you don't have an air fryer, it'll still be great heated in a microwave, but the crust may not stay crispy.