Preheat oven to around 200°C fan-forced. Line 2 large baking trays with baking sheets.
Put the butter in a pan cook the onions till they are golden brown. Remove and set aside to cool.
Skin sausages and put the meat in a large mixing bowl. Mash up the sausage meat with your hands. Add the finely chopped onions, breadcrumbs, garlic and cilantro to the sausage meat. Mix it all up with your hands.
Lay a sheet of pastry on a flat surface. Cut sheet in half horizontally. Spoon 1/8 of the mince mixture down along the long side of one pastry half, shaping mince into a long sausage shape. Brush opposite long edge with a little egg Wash.
Roll up pastry to enclose filling, finishing seam side down. Brush top of log with egg mixture. Cut into 6 short pieces. Place pieces, seam side down on prepared tray, 2cm apart. Repeat with remaining mince mixture, pastry and egg wash.
Bake for 25-30 minutes or until golden and cooked through.