Wash the asparagus and peel the lower third. Cut off the woody ends.
Juice the lemon. Place the lemon juice, salt and sugar in a saucepan with plenty of water and bring to the boil. Add the asparagus and cook for 5-6 minutes.
Remove the asparagus, cool under cold water and drain.
Melt the butter in a pan. Grate the cheese.
Carefully unfold the filo pastry sheets and divide them into 16 rectangles (approx. 8 x 10cm).
Brush the pastry with a thin layer of melted butter.
Top each rectangle with 1 ham slice and 1 asparagus spear. Sprinkle with some cheese and roll up, so that the asparagus tips are still visible.
Place the asparagus rolls on a baking tray lined with baking paper.
Brush the rolls with the remaining butter. Sprinkle with sesame seeds. Bake the asparagus rolls in a preheated oven at 200°C (180°C fan, gas 6) for 12-15 minutes until crispy.