Preheat the oven to 425°F. Place a 10-inch cast-iron skillet inside and allow it to heat for at least 5 minutes.
In a blender, combine the eggs, flour, milk, sugar, salt, and nutmeg. Blend until smooth.
Carefully remove the hot skillet from the oven and add the butter. Swirl it around to coat the bottom and sides evenly.
Pour the batter into the hot skillet and return it to the oven. Bake for 13 to 16 minutes, until the edges are puffed and golden brown and the center is set.
Remove from the oven, lift the Dutch baby out using a spatula, transfer to a serving dish, dust with powdered sugar, and serve with fresh berries.