You will need an 8 inch cast iron skilled for this recipe. Add all your ingredients except for the butter into a blender or food processor.
Pulse until a smooth batter forms. Let the mixture sit for 30 to 60 minutes - just to come to room temperature.
Put your cast iron skillet on the middle rack of your oven and preheat to 450F.
Take the preheated skillet carefully out of the oven and add the 4 tablespoons of butter, swirling the pan to melt the butter and coat the pan. Once the bottom of the pan is covered in butter, pour the batter into it and immediately return to the oven.
Bake until puffed and golden brown, about 18-20 minutes. DO NOT OPEN THE OVEN to have a look at it or you will deflate the baby!
Dust with lemon zest, powdered sugar and fresh berries if desired. Serve warm.