In a blender, combine the eggs, milk, flour, salt, vanilla, nutmeg, and maple syrup. Blend 1 minute, until smooth. Make sure no large clumps of flour remain. Make sure the batter is smooth, like crepe batter.
Melt the butter in a 10-12 inch cast iron skillet in the preheating oven for about 3 minutes until just melted. Pour the batter into the hot skillet. Place the skillet in the center of the oven and bake for 17-20 minutes or until the Dutch baby is fully puffed and lightly browned on top. (Be sure not to open the oven during the first 15 minutes of cooking or you might deflate the pancake.)
Let it cool for 2 minutes, slice, and then top with fresh berries and maple syrup or homemade berry sauce!