Method:
Preheat oven to 220°C.
Sift flour, baking powder and mustard powder into a mixing bowl. Stir in the cayenne pepper, thyme and biltong.
Rub in the butter until the mixture resembles fine breadcrumbs. Gradually stir in enough cold water to make a stiff dough. Roll out the dough on a lightly floured surface until it is approximately 2.5cm thick and transfer to a 36 x 26 x 5cm baking tin.
Mix together all the topping ingredients except the egg and set aside. Whisk the egg with a little water and brush the dough. Sprinkle the topping evenly over the prepared dough. Bake in a preheated oven for 15 minutes, then allow to cool. Cut into small squares and serve.