Place butter into a 10-12" cast iron pan (the smaller the pan, the bigger the puff) and place it in your oven to melt and simultaneously heat the pan.
Add all ingredients listed after the butter into a bowl or into the bowl of a blender. Whisk together or blend until smooth. Do not over mix or process. Rest the batter for five minutes to give the flour a chance to absorb the liquid, this will give the pancake a better texture overall.
Remove cast iron pan from the oven and carefully add batter to the pan.
Bake for twenty-five minutes.
Remove from the oven, slice into wedges and serve hot with berries, syrup, preserves, confectioners' sugar or a cinnamon-sugar.