Pre-heat the oven to 220°C.
Mash or rice your potatoes in a medium sized bowl.
Sift the flour, salt and baking powder into another bowl.
Rub the butter in until the texture of fine breadcrumbs.
In the bowl containing the mash stir in the milk and mustard.
Then add the grated cheese and ham.
Add the dry ingredients and mix with a fork, adding more milk if necessary. (I needed 4 more tbsp).
Knead lightly on a floured surface for a few seconds until smooth.
Roll the dough out to 18 cm (7”) circle.
Put on a greased baking sheet and mark into 6 wedges with a sharp knife.
Brush with milk or egg wash.
Bake for 20 minutes or until golden and cooked through.
Cool on a wire rack.
Serve warm or cold.