Preheat the oven to 350 degrees F.

Melt the butter in 9 to 10-inch cast iron skillet (or oven safe pan) over medium/high heat and add sugar. Gently stir until sugar starts to turn brown, about 3 to 5 minutes. Be careful not to burn the sugar, as it will continue to cook since the pan is hot. Bring the heat to low then arrange the apples, skin side down, neatly. Make sure the pan is well packed with apples. Cook for few minutes. Cover the pan with pie dough and cut the dough along the pan leaving about 1-inch overhang. Fold the overhang inside the pan. Put the pan in the oven for about 20 minutes. After cooking, leave the tartin in the pan for about 5 minutes. Cover the pan with serving plate and flip the pan over and voila! Serve hot with creme fraiche on the side or ice cream.