German Apple Pancake or Big Dutch Babies

I first learned this one from The Vegetarian Epicure, made with apples.  Later a friend served a similar dish using warm raspberries as a filling/sauce and told me the proportions she uses.  So easy and so good!

German Apple Pancake (or Big Dutch Babies)

This is an easy and special brunch or a "pancakes" for supper meal or a fun dessert.  Basically, you make a popover or pudding batter using these proportions:
1 egg: 1/4 C milk: 1/4 C flour (works fine with gluten free flours)
Use about 1 -1 1/2 eggs per person.

Start your oven to 450.
Melt butter in a big cast iron or pyrex pan.  (I always use my cast iron fry pan so can't vouch for glass but that's what the recipe says.  With pyrex, it might be sensible to melt the butter in the oven, not the stovetop.)
Mix the batter.
Pour batter in pan and bake about 20 minutes.
While it is baking, cook and sweeten whatever fruit you you would like, apples, raspberries, peaches, etc.
When the giant pancake is done, slide it onto a big platter, fill with warm fruit, fold in half and dust with powdered sugar.  Really yummy!