Preheat the oven to 180°C fan bake or 200°C conventional. Grease a 22cm pie or flan tin.
Roll the pastry sheets together and cut to line base and sides of prepared tin.
Squeeze the potato in a clean tea towel to remove any excess moisture.
Mix together potato, sausage meat, onion, carrot, apple, breadcrumbs, egg, tomato sauce and season with salt and pepper to taste.
Spoon sausage mix into the pastry-lined tin and spread evenly with a spatula.
To make topping: Mix breadcrumbs, cheese and parsley together and sprinkle over the pie top.
Bake in the preheated oven for 40-45 minutes until filling is cooked and topping is golden.