This frittata is a little airier than usual and one of the simplest dishes to make for brunch. I like to garnish it with crème fraîche, Aleppo pepper, and fresh herbs. Any kind of herb will work, but I like to use parsley, the working man's herb.
Preheat oven to 375 degrees F. Separate the yolks from the whites of two eggs. Place the whites in the metal bowl set on top of the dish towel (to prevent moving) and whisk to soft peaks. Set aside. In another bowl, whisk 4 eggs, plus the 2 leftover egg yolks. Use a Microplane to grate the garlic into the eggs. Season with salt and pepper and set aside.
For the filling: Heat a skillet over medium-low heat. Add 1 tablespoon butter and 1 tablespoon olive oil. Slice the leek in half lengthwise (make sure there's no grit!), then thinly slice across. Add leeks to the skillet along with another tablespoon of oil, a pinch of salt, and a few grinds of pepper. Cook, stirring, until the leeks begin to wilt but have not taken on any color; then add the vinegar. Toss, then stir the leeks into the eggs. Wipe the skillet clean; then add the remaining butter and teaspoon of olive oil over low-medium heat. Quickly re-whisk the egg whites, then fold into the frittata mixture. Pour eggs into the skillet and gently scramble until the eggs are set, then place in the oven for 8–10 minutes.
Finish the dish: Remove the frittata from the oven and garnish with dollops of crème fraîche, chopped parsley, and aleppo pepper.