1Preheat the oven to 425 degrees F (220 degrees C).
2In a large bowl, use an electric mixer to blend eggs, milk and vanilla. Add flour, sugar, salt and cinnamon; mix just until blended. Set aside.
3Melt butter in a 9x9 inch square pan. Arrange apple slices in the bottom of the pan, and pour the batter over them. Sprinkle brown sugar over the top.
4Bake for 20 minutes in the preheated oven, or until puffed and lightly browned.