Preheat the oven to 425F with a 9x13 or equivalent baking pan in it to heat with the oven.
Whisk together everything but the butter and set aside, it's great to do this in advance so all of the flour hydrates and there are no lumps. You can also do this in the blender or with a stick blender for large batches.
When the oven and pan are hot, take out the pan and add the butter, swirl it around until the butter has melted.
Pour the batter into the pan and bake for 10-15 minutes until the edges are golden brown and the baby is poofy.
Serve immediately with powdered sugar and lemon, it quickly deflates as soon as it out of the oven.