In a large bowl, mix your potato, swede/rutagaba, onion, steak, salt and pepper. Take one of your pastry circles, place it onto your work surface. Place a really good handful of the meat mix onto half of the circle, leaving a 2cm border around the edge. It'll look like a lot of mixture, but it needs to be packed full. Dot a little butter (from the 40g butter) on top of the meat and veg pile. Take your beaten egg, and using a pastry brush, paint a little of the egg around the edge of the circle. This will help the pastry stick together. Now, fold the other side of the pastry over the meat until the edges meet and you have a semi circle. Seal firmly and crimp with your fingers (I found a good method of crimping about 2 mins into this video
by the Cornish pasty association). Place your pasty onto your baking tray and make a little hole in the top using a sharp knife to let out the steam. Repeat with the remaining pasties. Brush the remaining egg wash over the top of the pasties and place in the oven for 50 minutes until golden brown.