Heat the oven to 200 degrees C. Remove pastry from freezer, if using frozen. Put the sausage meat, chives and a generous grind of salt and pepper into a large bowl. Mix well.
On a lightly floured surface, roll the pastry out into a thin rectangular shape (approximately 23cm x 30cm x 0.5cm). Divide the pastry by cutting horizontally across the middle to get 2 strips. Spread mustard down the middle of each strip. Roll sausage meat into 2 long even strips the same length as the pastry then place on top of the mustard.
Brush beaten egg along the long side of the pastry. Fold the pastry over the top of the sausage meat then seal all along the edge with a fork.
Slice each strip into individual sausage rolls about 4cm long each. This way you should get 16 in total but you can make them as small or as large as you wish.
Cut two short lines in the top of each roll. Place on a baking tray, brush with beaten egg then cook for 20 minutes or until golden brown and crispy.