Halve the puff pastry lengthwise and crosswise, diagonally halve the squares created, transfer to an oven tray lined with baking paper and chill for approx. 10 mins. Brush half the triangles with the beaten egg yolk.
Bake for approx. 10 mins. in the centre of an oven preheated to 200°C.
Peel the bottom third of the asparagus, halve lengthwise. Leave the asparagus to steep in salted water at just below boiling point for approx. 5 mins., drain and mix with the oil.
Filling & serving
For the filling, finely chop the rocket, grate a little lemon zest, mix with the cottage cheese and season.
To serve: Divide the cottage cheese mixture onto the 4 uncoated triangles, top with warm asparagus, then place the remaining pieces of pastry on top and serve immediately.