Sieve the flour add salt, mustard powder and cayenne. Dice butter into small cubes and rub in until fine breadcrumb texture. If it’s a hot day or you have hot hands you might need to refrigerate to prevent butter from softening.

Grate both of the cheeses (keeping a tiny bit back for topping) Stir lightly into the breadcrumb mixture. Make a well, add in egg yolk and a couple of tbsp of cold water. Cut in with a round bladed knife. To form a dough. Add a tiny bit more water to help combine if necessary.

Wrap and chill for a 5 minutes.

Bake in preheated oven at 190c for 10-15 minutes or until golden brown and cooked through.