Sieve flour into the bowl and add cubed, cold butter and mustard.
Rub in the butter until you reach breadcrumb-like consistency.
Stir in grated cheese and knead until mixture comes together.
Cover it in clingfilm and let it rest in the fridge for 5 minutes.
Preheat oven to 180°C and line baking sheet with grease proof paper.
Roll out the pastry into rectangle shape (approx 32x13cm). It should be approx. 0.5cm thick.
Cut into straws approx. 2cm wide.
Brush gently with beaten egg and sprinkle over some grated parmesan.
Bake for 10-12min until lovely and golden.