Cut the pumpkin into large chunks and steam for 7-10 minutes until tender. Mix the flour, baking powder and salt in a bowl.
Cut the butter into small chunks and rub it in with your fingertips. (You could do this in a food processor, but it hardly seems worth the washing up.) Stir in the grated parmesan.
Roughly crush the cooked pumpkin with a fork or potato masher – taking care not to reduce it to a smooth purée – then lightly stir in the grain mustard and a grinding of black pepper.
Add this to the flour mixture, then pour in the milk and water. Stir the liquids into the flour, season with black pepper and mix the ingredients carefully, taking great care not to overmix.
Turn the dough out on to a floured board and pat it into a circle, roughly 3cm thick. Using a 5-6cm biscuit cutter, make 12 to 14 scones and place them, well apart from one another, on a baking sheet.
Brush the top of each one with beaten egg, taking care not to let any drip down the sides (it will stop them rising), then bake for 12-14 minutes until they are golden.
Remove the scones from the oven and let them rest briefly before transferring them to a cooling rack. Eat them the day you make them, preferably warm and with some quince jelly.