3 ounce mixed grated aged cheese, such as 1/2 gruyère and 1/2 irish white cheddar
Directions
Preheat the oven to 350 degrees.
Heat a 10-inch cast-iron skillet over high heat until medium hot. Reduce the heat to medium. Add the butter and melt until bubbling, swirling to coat the pan. Add the diced potato and cook, stirring occasionally, until soft and lightly browned.
Meanwhile, crack the eggs into a mixing bowl and beat with a whisk until the yolks are completely incorporated into the whites. Beat them longer than you would normal scrambled eggs, so as to incorporate more air into them. (The air helps the frittata to bake up light and fluffy.)
Add the salt, pepper, thyme, and milk, and beat again until smooth and lightly frothy.
Once the potatoes are browned, add the leek and ham, and sauté for several minutes, stirring occasionally, until the leek is soft. Remove from the heat and add the beaten eggs on top of the potatoes, leek, and ham.
Top evenly with the grated cheese, then place the skillet in the oven. Bake for 15 minutes. Remove from the oven and serve in sliced wedges with any garnish and/or accompaniment you would like (such as herbs, beans, sour cream, fruit, toast, crackers and jam, etc.).