Melt your butter in a heavy-based saucepan or frying pan over a medium heat, add your finely chopped onion and fry for 3-5 minutes until it just starts to brown a little.
Add your crushed garlic, chopped sage and 2 tablespoons of cold water, keep stirring and once the ingredients start to sizzle, pop on the lid, lower the heat and allow to cook down for 3 minutes.
Remove and leave to fully cool.
Heat your oven to 170°C Fan/190°C/375°F/Gas mark 5 and line a baking tray with greaseproof (parchment) paper.
Skin your sausages by slicing along the side and peeling back the skin, place the meat in a large mixing bowl.
Add your grated apple, breadcrumbs and one lightly beaten egg and mix in with your hands. Then mix in your cooled onion mixture.
Season with salt and pepper and squidge the whole lot together with your hands so everything is equally mixed.
Roll your pastry into two halves measuring approximately 36cm x 14cm each.
Take half of your sausage meat mixture and spread it along the centre of one of your rectangles of pastry.
Lightly beat your other egg, then using your pastry brush, spread some over the edges of two long sides of pastry.
Press the edges together with a fork to secure then gently push the secured edge under the sausage roll a little to give a neat finish.
Cover with more egg wash and then cut the long roll in half and then each half into equal thirds.
Place the sausage rolls onto your covered baking tray, sprinkle over sesame seeds and cut three slashes across the top.
Repeat with your other rectangle of pastry.
Bake for 35-45 minutes until browned all over.
Remove to a cooling rack to cool.