Preheat your oven to 200C (400F).
In a bowl, combine all the ingredients (except mustard and pickles) to make the beef mixture.
Cut the puff pastry sheets in half.
Spread a layer of mustard down the middle of each pastry half.
Top with pickles, and then generously add a layer of the beef mixture.
Roll up the pastry tightly, ensuring all the yummy fillings are enclosed.
Place the sausage rolls on a baking tray lined with parchment paper.
Brush the tops of the rolls with a whisked egg or milk to help them brown nicely.
Bake in the preheated oven for approximately 25 minutes, or until golden brown and cooked through.