Preheat your oven to 180°C (350°F). Spray the muffin tin with non-stick spray or line with silicone liners to prevent sticking.
Whisk the egg whites in a large bowl until they are frothy and slightly bubbly, about 1 minute. This creates a light, airy base.
Add the chopped spinach and shredded cheese to the egg whites, then season with salt and pepper. Gently fold everything together until evenly distributed.
Pour the mixture into the prepared muffin cups, filling each about 3/4 full. Leave some space for the bites to puff up during baking.
Bake on the middle rack for 15-18 minutes, until the bites are puffed, slightly golden around the edges, and a toothpick inserted into the center comes out clean.
If the tops aren’t golden enough, broil for 1-2 minutes, watching carefully to prevent burning. The surface should crackle slightly and smell cheesy and fresh.
Remove the muffin tin from the oven and let the bites rest for 2 minutes. This helps them set and keeps their shape.
Gently transfer the bites to a plate or wire rack. Serve warm or at room temperature for a light, fluffy, and portable breakfast or snack.
