Egg White and Spinach Breakfast Muffins

Step 1: Preheat the Oven and Prep the Muffin Tin

Preheat your oven to 350°F (175°C) and let it fully come to temperature before you put anything in.

Generously spray a standard 12-cup muffin tin with non-stick cooking spray, making sure to coat the sides and the bottom of each cup — egg whites stick aggressively if you skip this step.

Set the prepared tin aside while you work on the filling.

Step 2: Sauté the Onion and Garlic

Heat the olive oil in a small skillet over medium heat until it shimmers — about 30 seconds.

Add the diced onion and cook for 3 to 4 minutes, stirring occasionally, until it softens and turns slightly translucent. You're not looking for color, just softness.

Add the minced garlic and stir for another 30 seconds until fragrant. It should smell incredible at this point. Remove the pan from the heat and set aside to cool slightly.

Step 3: Wilt the Spinach

Add the roughly chopped spinach to the same skillet you used for the onion and garlic — the residual heat is enough to wilt it gently.

Toss the spinach around for 1 to 2 minutes until it just wilts down and turns bright, deep green. It will reduce dramatically in volume, which is exactly what you want.

Let the spinach and onion mixture cool for a few minutes so it doesn't cook the egg whites when you combine them.

Step 4: Mix the Egg White Base

Pour the liquid egg whites into a large mixing bowl or large measuring cup with a pour spout — the pour spout makes filling the tin much easier.

Add the salt, black pepper, garlic powder, and crushed red pepper flakes if using. Whisk everything together until the seasoning is evenly incorporated.

The mixture should look uniformly white and slightly frothy from the whisking — that's a good sign.

Step 5: Fill the Muffin Cups

Distribute the cooled spinach and onion mixture evenly among the 12 muffin cups — roughly 1 heaping teaspoon per cup.

Sprinkle a small pinch of shredded mozzarella into each cup on top of the spinach mixture.

Slowly pour the seasoned egg white mixture into each cup, filling them about three-quarters of the way full. Leave a little room at the top — they will puff up as they bake.

Step 6: Bake Until Set

Place the filled muffin tin in the center rack of your preheated 350°F oven.

Bake for 18 to 22 minutes, until the tops are set and no longer jiggle when you gently shake the pan. The edges should be pulling slightly away from the sides of the tin, and the tops should look matte — not glossy or wet.

A few golden spots on top are totally fine and actually a sign of good flavor development.

Step 7: Cool and Release

Remove the tin from the oven and let the muffins cool in the tin for at least 5 minutes before trying to remove them.

Run a thin butter knife or small offset spatula around the edge of each muffin to loosen it, then gently pop each one out. They should release cleanly if you greased the tin well.

Serve warm immediately, or let them cool completely on a wire rack before transferring to an airtight container for meal prep storage.