Heat your waffle maker. A mini waffle maker works great for sandwich-sized chaffles.
Preheat it until the indicator light shows it’s ready. Lightly grease with butter or oil spray.
Mix the chaffle batter. In a bowl, whisk 2 large eggs with salt and pepper. Stir in the shredded mozzarella (and Parmesan if using).
The mixture should be thick and well combined.
Cook the first chaffle. Spoon about half the mixture onto the hot waffle maker. Close the lid and cook for 3–4 minutes, until golden and crisp at the edges. Avoid opening the lid too early.
Cook the second chaffle. Repeat with the remaining batter.
Place finished chaffles on a wire rack so steam doesn’t make them soggy.
Cook the egg filling. Heat a small nonstick skillet over medium. Melt 1 teaspoon butter. Crack in 1 egg and season with salt and pepper.
Cook sunny-side up, over easy, or scrambled—your choice. For a neat sandwich, scramble lightly and shape into a round patty with a spatula.
Add the cheese. Place a slice of cheese over the cooked egg for 20–30 seconds so it melts. If using extras like bacon or tomato, warm them in the pan briefly.
Assemble the sandwich. Layer egg and cheese between the two chaffles.
Add optional toppings like avocado or hot sauce. Press gently so everything holds together.
Serve hot. The best texture is right away—crisp outside, gooey center. If you need to hold it, keep it on a wire rack in a warm oven for a few minutes.