In a blender, add the milk, eggs, flour, sugar, vanilla and salt. Blend for about 20 seconds until well combined, scraping down as needed. Let batter rest for about 20 minutes.
Place a cast iron skillet in your cold oven and then preheat the oven to 425 degrees with the pan in it.
Carefully remove the hot skillet from the oven using pot holders and place the butter in the skillet. Use a brush to spread the melted butter all around the pan including up the sides.
Pour the batter in to the buttered skillet and return the pan immediately to the oven.
Bake for 15-17 minutes or until puffed and golden. (It will be darker brown around the edges!)
Serve warm with whatever toppings you want and a good sprinkle of powdered sugar!