In a large bowl, combine lamb, onion, pine nuts, harissa, currants, parsley and cumin and season to taste with sea salt and freshly ground black pepper (check seasoning by frying a little of the mixture in a frying pan and taste). Spoon mixture into a piping bag (you won’t need a nozzle).
On a lightly floured work surface, roll out puff pastry to a 3mm-thick rectangle. Pipe lamb mixture along longest edge, roll over pastry to enclose, brush eggwash along pastry edge and press to seal. Trim along length of pastry and repeat with remaining mixture and pastry.
Preheat oven to 200C. Brush sausage rolls with eggwash, scatter with sesame seeds and cut into 5cm lengths. Place on baking paper-lined oven trays and bake for 15-20 minutes or until golden. Serve immediately. Unbaked sausage rolls can be frozen for up to 1 month. Bake from frozen at 200C for 25 minutes or until golden and cooked through.