Preheat the oven to 180C/gas mark 4.Sprinkle a clean work surface with flour. Lay out the pastry sheet, with the longer edge towards you. Lightly spread the pastry sheet with Marmite. (It’s easier if the pastry’s cold.)
Cover the whole pastry sheet with the grated cheddar. Fold in half from the top down and, coating the rolling pin with some flour, gently roll out the piece to lengthen it.
Line the largest baking tray you can find with greaseproof paper (you can use the paper the pastry is packed in). Carefully transfer the pastry to the chopping board and use your sharpest knife to cut the pastry into batons about 1.5cm wide (or however big you like).
Lay the straws next to each other on the tray. Beat the egg in a cup and, with a pastry brush, coat each baton with egg. Sprinkle with parmesan, chilli flakes and a grinding of black pepper then bake for 20 minutes until golden and crisp.