A frittata pan is specifically designed for cooking frittatas. It is a dual handled pan (usually nonstick) with a hinge that allows the pan to be opened or closed with a lid. The egg mixture is poured into the bottom portion and additional ingredients placed on top. After the bottom begins to cook the frittata is lifted slightly with a spatula so any additional egg rolls off the top and cooks on the bottom. This way the ingredients are only baked slightly into the top. Then the lid is closed and the frittata is cooked to the desired consistency, traditionally well done.
See Judy Baxter's, Making a frittata in 39 photographs!