Sift the flour, mustard, cayenne and salt into a
bowl and rub in the fat until the mixture resembles
breadcrumbs.
Stir in three-quarters of the cheese,
the egg and enough milk to mix to a soft dough.
Turn
on to a floured surface, knead lightly and roll out
to 2 cm/3/4 inch thick. Cut into 5 cm/2 inch
rounds and place on a floured baking sheet.
Brush
with milk and sprinkle with the remaining cheese.
Bake in a preheated oven, 200°C (400°F), Gas Mark 6,
for 15 minutes. Transfer to a wire rack to cool.
Serve with butter.