Preheat the oven to 375 degrees. Prepare apples if you have not done so, peeling, coring and cutting the apples into 8 slices.

In the skillet, melt together the butter and sugar, whisking over medium high heat until the mixture is smooth and begins to simmer. Whisk it constantly to form a caramel sauce. If it is darkening too quickly, reduce the heat. Whisk about 5-7 minutes to form the caramel.

Lay the apples into the bottom of the skillet, into the caramel in a tight circular formation. They should overlay each other slightly as they will continue to shrink while cooking. Line the outer rime of the skillet with additional apples to form a ring to hold them together if you have extras.

Lay the sheet of thawed puff pastry over the top of the apples and tuck the edges down around the edges of the skillet to hold the apples together. Poke the puff pastry with a fork in several places.

Place the skillet in the oven and bake for approximately 40-45 minutes or until the puff pastry is deep golden brown. Remove the skillet from the oven and allow it to cool at least 10 minutes prior to turning it out on a serving plate. Some apples may have stuck to the bottom, so carefully place them back into the tarte.

Serve with ice cream, ala mode style if desired!