Start by preparing the filling for the strudel by peeling and coring the apples. Cut the apples into thick slices and place in a saucepan with the sultanas, caster sugar, water, orange zest and cinnamon. Cook for a few minutes, just to slightly soften the apples. Remove the saucepan off the heat and leave apples to cool. Next, lay the filo pastry on a floured work surface and cover with a tea towel to prevent it from drying out. Take one piece of filo pastry, and brush it all over with the melted butter. Place another piece of filo on top, and brush again with some more butter. Place the third piece of filo on top, giving you 3 layers of filo pastry on top of each other. Brush again with some more melted butter. Roll out the marzipan to a long strip, 3 inches wide, and place down the middle of the filo pastry. Add the cake crumbs to the cooked apples and mix well. Pile the apple mixture on top of the marzipan, almost like a large sausage. Fold the extra filo pastry on one side over the apple mixture. Brush this with melted butter, and then fold the remaining filo pastry over again. Close up the ends by folding the excess pastry under the ends of the strudel to seal. Brush with the remaining butter and place the strudel on a large baking tray. Bake in the oven at 200`c, for 30-40 minutes, or until the strudel is golden brown in colour. Remove the apple and cinnamon strudel from the oven and dust with icing sugar. The apple and cinnamon strudel can be served warm or cold, cut into thick slices.