1. Peel the apples and cut them into small pieces.
2. Boil them with two fingers of water and the juice of half a lemon, until they are very tender.
3. Remove from water.
4. Let cool.
5. Cut a wide strip of puff pastry.
6. Fill with two tablespoons of apple, cinnamon to taste and chopped walnuts.
7. Close the puff pastry with a fork so that the filling doesn't come out.
8. Brush over with agave syrup.
9. Cook in an air fryer in oven mode, at 180°C/350ºF for 8 minutes. Let cool.