Place the ingredients for the batter in a blender and blend until creamy and foamy, about 1 minute.
Place the butter in the skillet and put the skillet in the oven until the butter is melted and sizzling.
Pour the batter into the center of the hot skillet so that the batter runs to the edges and some of the butter is pushed onto the top of the batter. Bake for 15 to 20 minutes, until the Dutch baby is puffy and dark brown. The center should be just set. The Dutch baby is likely to rise in a lopsided fashion and will deflate somewhat as it cools
Serve hot from the oven, topped with a few fresh berries and a dusting of cinnamon or powdered sweetener, if desired. Leftovers can be eaten cold.