Heat oven to 400°. Add butter to a 12-inch cast-iron skillet and place in oven to melt.Advertisement
Meanwhile, whisk eggs and next 4 ingredients in a large bowl. Carefully remove skillet from oven and swirl so butter coats bottom of pan. Pour in egg mixture and return pan to oven. Bake 18 to 20 minutes, until puffed and golden. Sprinkle with confectioners' sugar and serve.