Gather your equipment: a 10-inch ovenproof skillet, a whisk, a spatula, and a mixing bowl. Preheat your oven to 180°C (350°F).
In the mixing bowl, whisk the egg whites until they become frothy and slightly bubbly, about 30 seconds. Season with a pinch of salt and pepper.
Chop your chosen vegetables into small, uniform pieces so they cook evenly and won’t weigh down the delicate eggs. Set aside.
Heat the olive oil in the skillet over medium heat until shimmering and fragrant. Add the chopped vegetables and sauté until just tender, about 3-4 minutes. You’ll notice the vegetables releasing their aroma and softening.
Pour the whipped egg whites evenly over the sautéed vegetables in the skillet. Let cook undisturbed for about 2 minutes, watching as the edges start to set and turn slightly golden.
Reduce the heat to low and transfer the skillet to the preheated oven. Bake for 10-12 minutes, until the top is puffed, lightly golden, and a toothpick inserted in the center comes out clean. You’ll hear gentle bubbling and see the surface rise.
Remove the skillet from the oven and let the frittata rest for about 2 minutes. The residual heat will finish setting the structure, and the surface will look fluffy and inviting.
Sprinkle with cheese and chopped herbs for added flavor, then slice into wedges directly in the skillet or transfer to a plate. The final dish should be tender, airy, with a lightly crisp, golden top and vibrant vegetable accents.
