Preheat oven to 180°C. Combine all ingredients for the filling (everything above puff pastry) in a large bowl. Work them with your hands until they turn into a sticky, almost paste-like mixture. Set aside. You may like to wash your hands here!
Cut the thawed pastry sheets in half. Take ¼ of the mixture, shape it like a sausage and place it along the long side of one of the pastry sheets. Roll up and cut into 4 pieces. Repeat with the remaining half sheets.
Place sausage rolls seam side down onto a lightly greased baking tray. Brush tops with milk and sprinkle with the salt and sesame seeds, if using. Bake for 20-25 minutes, or until golden brown.