Then you sprinkle about 1 cup of sugar evenly on the bottom of an oven-proof skittle/frying pan. Dot that with 4 tablespoons of butter and then arrange the apples on top. The round part (outside) of the apples should be facing the bottom of the pan - you will eventually turn the entire thing upside-down and the bottom will become the top.
Then you top the entire thing with a piece of pie dough (or puff pastry - both are absolutely delicious options) and tuck the edges down.
Bake it in a 375 degree oven for about an hour or until the apples are tender when you poke it with a fork.
Let it rest for about 5 minutes and then place your serving plate on the skillet and (very quickly and carefully) flip the tatin upside-down onto your plate.