A riff on the Spanish omelet or tortilla española, this vegetarian Mexican potato omelet makes a gratifying breakfast that's quick and easy to make.
Prepare the egg and cheese mixture
In a large mixing bowl, whisk the eggs until the yolks are completely broken up and incorporated. Stir in half of the mixed cheese, tomatoes and cilantro. Set aside.
Parboil the potatoes
In a large heavy-bottomed pot, cover the cubed potatoes with cold water and bring to a boil over high heat. Boil the potatoes for 5-6 minutes, remove them from the heat and drain in a colander for 2-3 additional minutes. This step is optional — you can certainly cook the raw potatoes in a skillet — but parboiling the potatoes guarantees even cooking and an overall better omelet.
Cook the potatoes and onions
In a cast iron skillet (or other broiler-proof pan) over medium-low heat, cook the diced potatoes in 1 tablespoon of the olive oil for about 5-7 minutes, stirring occasionally, until the potatoes turn golden brown and tender. Add in the onions and garlic and cook for an additional 5 minutes until the onions are almost tender and the garlic becomes fragrant.
Preheat the broiler on your oven to high, making sure the top rack is at its highest setting (about 4 inches form the the top of the oven).
Finish the omelet
Add the remaining oil to the skillet, and pour the egg and cheese mixture over the potatoes, gently mixing and spreading the egg with a spatula. Cook the potato omelet for 8 to 10 minutes until the center is almost set, lifting the edges of the eggs occasionally to let the uncooked egg flow underneath. Top with the remaining cheese and broil in the oven for 2 to 3 minutes or until the the omelet is completely set and the cheese is golden brown. Garnish with sour cream.