Bring a large cast iron skillet to medium heat. Add 2 tablespoons of oil. When oil begins to heat, add both varieties of diced potato. Stir potatoes to coat with oil, then let fry undisturbed, to encourage browning, about 5 minutes. Adjust heat as needed to prevent burning. When potatoes have begun to brown, use a spatula carefully lift and flip potatoes, to uncrowned side. Let them sit undisturbed for another 2-3 minutes.
Notes **to fry an egg**: add remaining oil to a non stick or stainless still frying pan. Bring pan to medium heat. Crack a whole, unscrambled egg into to the pan. Allow egg to pop and edges to begin to rise before flipping, about 2 minutes. Season with salt and pepper, and use a spatula to gently flip egg over. Repeat seasoning. Cook until desired donees and serve immediately.