chloeben: Look at the shape of the edge of the pie. An easy way to do this is to use your two first fingers to press the top and bottom layers of pastry together.
Another nice touch is to brush the top of the pie with a beaten egg or cream if you have a bit to spare, this makes for a nice gold crust. Also on a savoury pie I cut leaves from the off cuts of pastry and put them on the top after brushing.
I gave this 4 stars even though I did not do this recipe, mine is almost the same without milk and potato, I therefore predict it would be very yummy.