Slice the butter in the pan and melt it in the preheating oven.
While the butter is melting, in a mixing bowl, beat together the milk, eggs, flour, and vanilla.
When the butter is bubbling, remove the pan from the oven and pour the batter into the bubbling butter.
Return the pan to the oven and bake for 20 minutes.
Serve immediately.
Notes:
It's safest to put the pan in the oven 25 minutes before breakfast, especially at preps. The convention-sized pans have an effect on the cooking time too - it works best to only cook 1 convention-sized pan in a commercial oven.Make Ahead: It's very quick to whip the batter up, but you can easily prepare the batter the night before, cover with plastic wrap, then just give it a stir in the morning before pouring it into the hot butter to bake.