You will need one 10-inch cast iron pan. Wash and prick potatoes, microwave for three to four minutes. Brush sides and bottom of pan with olive oil. Slice potatoes thinly and use them to cover the bottom of the pan. Turn when lightly browned until all potatoes are golden.
Mix all other ingredients together in bowl. With potatoes covering bottom of pan, pour liquid mixture slowly over potatoes.
Cook over low heat until sides are cooked. Place pan under grill and cook until egg mixture is thoroughly cooked - usually within 5 minutes. Your frittata should look like a 'golden' pizza. Slice and serve immediately with diced tomatoes.