Preheat oven to 325F.
Prepare the sausage mixture – mix the ground sausage, seasonings, breadcrumbs, and onion together in a large bowl. Set aside.
Roll out one square (half of the package) the puff pastry into a large rectangle, about the size of a sheet pan.
Cut the puff pastry lengthwise into two equal halves.
Spread each sheet of puff pastry with a tablespoon of dijon mustard.
Fill each rectangle of pastry with 1/4 of the sausage mixture, reserving the second half of the sausage mixture for the second half of the batch.
Brush one edge of the puff pastry with beaten egg and fold the puff pastry over. Crimp the edge of the roll with a fork to seal it. Brush both rolls with egg wash.
Cut the rolls into 12 equal pieces, scoring the top of each piece with the knife.
Bake for 30 mins or until golden brown.