Preheat oven to 220C (430F) and line a baking tray with baking paper.
In a large bowl, sift flour, baking powder, baking soda, salt, and sugar. Add thyme, cayenne pepper (if using) and garlic powder. Whisk until well combined.
Using your finger tips, rub in the butter until fine crumbs form (the mixture will be dry). Add cheese and mix to combine.
In a small jug, combine the eggs, milk with vinegar and mustard and whisk. Add this to the flour mixture and using your hands, bring the dough together until the dough is wet and slightly sticky.
On a floured surface, press the dough into a circle shape about 2cm thick. Cut in 8 triangles and place on prepared baking tray. Brush each scone with any remaining liquid from the egg and milk and sprinkle additional cheese on top.
Bake for 10-12 minutes or until golden brown.
Notes
* Scones are best eaten the day the are made however they keep well when frozen in an airtight container or bag. Simply reheat in oven or microwave.