Pre-heat your oven to 200C Fan/400F/Gas Mark 6, and line a baking tray with baking paper
Stir the self raising flour, salt, baking powder and if using, the mustard powder or other spices, together a mixing bowl
Add the butter and rub it into the flour with your fingers, a pastry blender or a fork ,until it resembles breadcrumbs. You can also use a food processor to do this step
Add the cheese to the flour mixture and stir it in
In another bowl, or in a jug, whisk together the egg and milk. Add it to the flour mixture
Bring the mixture together to form a dough, being careful not to overwork or knead it too much
Using your hands, pat it out into a flat disc shape onto a clean work surface (or a silicone mat) dusted with flour. Aim for it to be about 2cm thick. Cut out the scones using a round cutter, size of your choice (I used a 2.5" one). Push the cutter straight down and do not twist it
You will need to re-pat out the dough to use it all up
Place the scone rounds onto the baking tray, brush them with the beaten egg and sprinkle with the cheese
Bake for 12-14 minutes or until golden brown and risen. Remove from the oven and allow to cool, you can eat them warm or cold
Store in an airtight container and eat within 2 days. They can also be frozen