Preheat the oven to 200ºC, gas mark 6.
Mix together flour, baking powder, mustard powder, chopped sage and salt.
Use your fingers to rub in the butter until the mixture resembles fine breadcrumbs.
Fold in the parsnips and 175g of the cheese, and gently stir in the egg and milk until the mixture is just combined.
Flour a work surface and roll out the dough to a 3cm thickness.
Cut out the scones and arrange the in a large circle on the lined baking tray, making sure they overlap slightly.
Brush the surface of the scones with the remaining milk, sprinkle over the remaining 25g cheese and bake for 20-25 minutes until golden brown.
Cool on the tray for 10 minutes, then transfer to a cooling rack to cool further.
Mix the butter with the honey. Sprinkle over the salt, then mix again.
Place the mixture onto a rectangle of baking parchment .
Form into a neat 8cm-long log.
Tightly wrap it up and roll until smooth, then secure with a knot at each end. Place it into the fridge to chill.
The scones are best served while still warm, with slices of the honey butter.