Preheat the oven to 450 degrees. Place a 9 or 10 inch cast iron skillet in the oven. Meanwhile in a blender combine the eggs, milk, flour, vanilla, sugar, salt, and the orange zest. Blend until smooth. The batter will be thin. Then remove the skillet from the oven. Add the butter and place back into the oven until the butter is melted. Then remove the skillet from the oven and pour the batter into the hot skillet. Place the skillet back in the oven and bake for 18 to 25 minutes, until it is puffy and golden brown. Serve imediately with a light dusting of powdered sugar and some fresh berries.