Pulse flour, baking powder, salt, butter and egg yolk in a food processor until breadcrumbs form.
Gradually add water until a dough forms, then wrap and chill for one hour.
Boil chopped swede and potato for 4-5 minutes until tender, then drain and refresh.
Preheat the oven to 180°C.
Roll out pastry and cut a large disc using a dinner plate.
Layer onions, steak, potatoes, swede, and parsley down the center of the disc.
Crimp the pastry edges together over the filling and seal with beaten egg.
Make a small hole in the top and glaze the pasty with remaining egg.
Bake on a tray for 25-30 minutes until golden-brown.