Pre-heat oven to gas 4, 180ºC, fan 160ºC. Place pork, plums, jam, seasoning and sage in a large bowl, mix together well.
Roll out the pastry and using approx 17cm (6½in) bowl/saucer cut out 4 circles, re-roll and you should be able to cut one more.
Place a large spoonful of the mixture into the centre of the circle, lightly brush the edges of the pastry with a little water and fold the pastry around the filling. Press edges together and seal with a crimp pattern.
Brush with egg and milk glaze, and place on a non-stick baking tray (or use baking parchment). Bake in a preheated oven for about 25-30 minutes until pastry is golden brown.
Serve hot or cold, great with a fruity relish or chutney.
Haven't got time to cook this from scratch?
Try our ready-made version - Ginsters cornish pasty.