Follow these detailed steps carefully to ensure your veggie egg white muffins come out perfectly light, fluffy, and full of flavor every single time. The process is straightforward, making it an ideal recipe for batch cooking and meal prepping.

Step 1: Preheat and Prepare Your Pan
First things first, preheat your oven to 375°F (190°C). This is a critical step; placing the muffins in a properly preheated oven ensures they cook evenly and rise correctly. While the oven is heating, prepare a standard 12-cup muffin tin. You must grease it very generously. Use a non-stick cooking spray, making sure to coat the bottom and all sides of each cup thoroughly. Alternatively, you can use a pastry brush to apply a thin layer of olive oil or melted butter. If you skip or skimp on this step, your muffins will stick, so be thorough!

Step 2: Prepare the Vegetables
Finely dice your red bell pepper and red onion. The key here is to make the pieces relatively small, about the size of a pea. This ensures they cook through and distribute evenly within each muffin cup. For the baby spinach, you can either chop it roughly or leave it as is.

Step 3: Distribute the Fillings
Now, it’s time to build the foundation of your muffins. Evenly distribute the diced red bell pepper, diced red onion, and fresh baby spinach among the 12 greased muffin cups. Don’t worry if the spinach seems to be overflowing; it will shrink down significantly as it bakes. After the veggies are in, sprinkle the shredded mozzarella cheese evenly over the top of the vegetables in each cup.

Step 4: Prepare the Egg Mixture
In a large bowl or a 4-cup measuring cup (which is great for easy pouring), pour in your liquid egg whites. Add the garlic powder, onion powder, dried oregano, black pepper, and salt. Whisk the mixture vigorously for about 30-60 seconds. You want to incorporate some air into the egg whites, which will help make the final muffins lighter and fluffier. Ensure all the seasonings are well combined.

Step 5: Fill the Muffin Cups
Carefully and slowly pour the seasoned egg white mixture over the vegetables and cheese in each muffin cup. Fill each cup about three-quarters of the way full. It’s important not to overfill them, as the muffins will puff up considerably during baking and could spill over, creating a mess.

Step 6: Bake to Perfection
Place the muffin tin on the center rack of your preheated oven. Bake for 20-25 minutes. You’ll know they are done when the tops are firm to the touch, and they have puffed up and are lightly golden brown around the edges. A good test is to insert a wooden toothpick or a knife into the center of one of the muffins; if it comes out clean, they are ready.

Step 7: Cool and Release
Once baked, remove the muffin tin from the oven and let it sit on a cooling rack for at least 10-15 minutes. This is a crucial step! The muffins will deflate slightly as they cool—this is completely normal. Allowing them to cool in the pan helps them set up and makes them much easier to remove without breaking. After they have cooled for a bit, use a thin silicone spatula or a butter knife to gently run around the edge of each muffin to loosen it before lifting it out. Place them on the wire rack to cool completely before storing.