Preheat oven to 350˚ F.
Combine the spring onion, leek, and onion in a medium bowl. Add the asparagus EXCEPT the spears. These will be placed on top of the egg bake.
Grate the potato using a large hole grater.Add to the bowl holding the onions along with the Serrano pepper.
Heat up the oil in a large sauté pan over medium high heat, and add the prepped vegetables along with 1 1/2 teaspoons kosher salt, and the Herbes de Provence. Sauté uncovered for five minutes. Reduce the heat and cover, and cook for an additional 10 minutes. Cool slightly.
When the artichokes are tender, remove from the water and add the asparagus spears to cook for 5 minutes, or until just tender.
Whisk 8 whole eggs plus 4 yolks together in a large bowl. Add the milk and cheeses. Gradually whisk in the vegetable mixture one large spoonful at a time, unless the onion mixture is close to room temperature. If the vegetables are at room temperature, it's fine to whisk in them into the eggs all at once.
NOTE: This recipe can be made ahead to this point, with all components wrapped and refrigerated overnight.
Whip 4 egg whites to a medium-firm peak, and fold into the egg mixture using a large spatula. It's best to fold the egg white in one-third at a time for best results.
Butter or oil a baking dish, and pour the eggs in. Top with the cooked artichokes and asparagus spears.
Place the baking dish on a baking sheet and bake on the middle rack for 75 minutes, or until firm in the middle. The eggs will begin to brown after the first half hour, and I recommend covering the dish with foil at this point for the remaining baking time.
Allow to sit for 15 minutes before serving.