1. Cut the apples into small cubes. In a large frying pan, melt the butter and sauté the apples over medium heat until they soften slightly and release their aromas, without turning to mush.
2. Add the cinnamon, breadcrumbs, raisins, coarsely chopped walnuts, and cognac. Mix well and let the filling cool down slightly.
3. Lay the first sheet of puff pastry on a work surface and prick it lightly with a fork. Place half of the filling along the length and carefully roll it up into a log. Repeat the same process with the second sheet.
4. Transfer the strudels to a baking tray lined with parchment paper. Brush the surface with a little water and sprinkle with sugar.
5. Bake in a preheated oven at 180°C (using the resistance setting) until nicely browned and crispy, about 35–40 minutes. Let them rest for a few minutes before cutting and serve warm.
