Preheat your oven to 425F. Place the butter in a 9” cast iron or oven-proof skillet and place the skillet in the oven as it preheats.
Mix the remaining ingredients together in a food processor until smooth and frothy. Pour the batter into the hot, prepared skillet and return it to the oven. Bake the Dutch Baby for 20 minutes.
Remove the Dutch Baby from the oven and slide it onto a large plate. Dust it with powdered sugar and serve with a squirt of lemon juice. (And more butter, if desired.)
Notes
If you are doubling this recipe to make Dutch Babies for more than two people, just be sure to melt new butter in the pan, in the oven, for a minute or two before making another Dutch Baby. This will re-heat your skillet and ensure that your baby doesn't stick.