1. In a 10-inch nonstick, ovenproof skillet over medium heat warm oil. Add potatoes, and sprinkle with salt and pepper. Cook potatoes, flipping once, until both sides are soft and golden brown, about 5 minutes.
2. In a medium bowl add eggs, milk, cheese, and tomatoes. Whisk well to combine.
3. Pour eggs over cooked potatoes; stir to combine with potato slices, using a rubber spatula. Cook until edges are set, and the center is slightly wiggly. Transfer to oven and bake for 1-3 minutes, until the top is golden brown.
4. Remove from oven with a pot holder. Slide frittata onto a cutting board and slice frittata into 4 pieces. Serve and enjoy!