Sauté mushrooms separately for 3-4 minutes before adding to the egg mixture to remove excess moisture and concentrate their umami flavor, preventing soggy muffins.

After wilting fresh spinach, wrap it in a clean kitchen towel and squeeze firmly to remove excess water, which prevents the muffins from becoming watery and rubbery.

Crumble feta cheese directly into the muffin cups last, just before pouring the egg mixture, so it doesn't distribute unevenly and creates pockets of creamy, tangy flavor throughout.

Tear fresh basil and sprinkle it on top immediately after removing muffins from the oven while they're still warm to capture its delicate aroma and bright taste without losing potency from heat.

Insert a toothpick into the center—it should come out clean or with just a tiny bit of moist egg; they'll continue cooking slightly as they cool, so avoid over-baking for a custardy interior.