Unfold the puff pastry sheets then cut along the fold lines of each sheet to form 6 equal squares for a total of 12 squares. Brush each square with mustard. Divide sausage into 12 pieces then roll into small logs. Place one log on each square. Roll pastry around the sausage then seal with a bit of beaten egg. Place rolls onto an ungreased baking tray then brush the tops with the rest of the egg.
Bake for 20 minutes in the preheated oven or until the rolls are puffed and golden. I usually watch after 10 minutes or so to make sure they don't burn.