- Preheat the oven to 350 degrees F (175 degrees C).
- Spray a muffin tin with cooking spray.
- Mix egg whites, Cheddar cheese, spinach, hot sauce, salt, and pepper in a bowl.
- Ladle mixture into the muffin tin, filling each cup 3/4 the way full.
- Bake in the preheated oven until a knife inserted in the center of a muffin comes out clean, 20 to 25 minutes. Serve warm or cooled.