Preparation

• Heat the oven to 400ºF. Whisk the eggs vigorously with the mustard, milk, salt, and pepper. In an ovenproof 10-inch enameled cast-iron or nonstick skillet, heat the olive oil over medium heat. Add the onion and potatoes, season with salt, and sauté until tender. Turn the heat to medium high and then pour the eggs into the pan. Let the eggs set for several seconds, and then, with a heatproof spatula, gently stir the eggs, starting from the center. This will make the frittata puff up more in the oven. Lift the edges so that the eggs flow to bottom. When the frittata is half-set, sprinkle on the ham. Transfer the pan to the heated oven. Cook for about 10 minutes, until puffed and golden.