Preheat oven to 400°F. Place the butter in a 9 inch cast iron skillet or cake pan and put in the oven.
In a medium bowl, whisk together the eggs, milk, flour and salt until combined. When butter is melted, remove pan from the oven and swirl butter around until it coats the bottom and the sides. Pour the batter into the pan and place it back in the oven.
Bake until puffed and golden, about 25 to 30 minutes. Serve immediately with fresh lemon or orange juice, powdered sugar, and fresh fruit.