Puffy Oven Pancake from Risa

I usually make my recipe from Betty Crocker book but when Risa came to visit she made a version that was much better than mine. This is it:

let 1/2 stick of butter melt in oven  in 9x13 pan while preheating to 400 degrees.
6 eggs
1 c. flour
1 c. milk

Mix three ingredients with beaters or in blendtec.
add 1 tsp. salt and three dashes or about 1/2 T. ? of vanilla.
cook for 22 min.