Preheat an oven to 450ºF. Line a large baking sheet with parchment or silicon mat.
Put the flour, baking powder, salt, dried herbs, mustard and cheese into the food processor and pulse a couple of times, just enough to combine everything. Add the butter, diced and pulse until the mixture resembles breadcrumbs.
With the food processor running, pour in the milk and water in a steady stream. The dough will start to come together very quickly and as soon as it starts to ball up, stop the processor.
Add the walnuts and pulse just a couple of times to combine the mixture. Remove from the food processor to a well floured work surface.
Roll out the dough to about 3/4" thickness then cut out circles with a floured 3" cutter. Place the scones on the baking sheet then reroll the remaining dough and cut more until all is used. This should yield about 12 scones.
Brush the tops with an egg wash made with the beaten egg and 2 tbsp milk, then sprinkle the tops with more sharp cheddar.
Bake for about 17 minutes in the center of th4e oven. Check to be sure they are not burning on the bottom at the 14 minute mark
