Proceed to the filling. Cut a thin layer of peel from apples, remove the core. Cut into thin slices, add cinnamon and sugar. Mix it. Then put the apple slices in a saucepan, add the soft butter, cinnamon and mix. Keep on low heat under the lid for about 5-15 minutes (the time depends on the variety of apples). The pieces should soften a little, but keep their shape