Preheat oven to 425°. In a blender, or large bowl, mix eggs, milk, flour, white sugar, vanilla, salt, and cinnamon until blended. Batter will be slightly lumpy.
Melt butter in a 12” fluted porcelain dish, or a 9 x13 inch baking dish. Add apple slices and return to oven until butter sizzles, but not browned.
Remove dish from oven and immediately pour batter over the apples and sprinkle with brown sugar. Bake on middle rack for 20 minutes until puffed and brown. Serve immediately.