Whisk together the milk, flour, sugar, and eggs until smooth.
In a large skillet (12 x 9) (like a cast iron pan if you have one), melt the butter over medium heat until it is bubbly, and tilt the pan until the butter coats the bottom and sides of the pan.
Then lay out the thin slices of apple making sure to cover the bottom of the pan, but not enough to layer them. The apples should be spread out only in one layer.
Sprinkle on the brown sugar and cinnamon.
Pour the pancake batter into the skillet and let it cook for about 1 minute, without stirring!
Then place the skillet into the oven and bake for about 15 minutes.
The pancake will be done when it is golden brown and puffed up.
Once the pancake is done, sprinkle generously with icing sugar and serve immediately (while it’s puffed up).