Heat one tablespoon of butter in a medium saucepan then add the shallots and cook until transparent.
Add the beef mince and sprinkle with parsley. Remove from heat and let cool.
Add the egg to the mince mixture then mix well. Form 4 sausages with the meat mixture.
Cut the puff pastry sheet into four rectangles. Add a sausage to the lower part of a puff pastry rectangle and then fold the puff pastry over the meat and pinch the pastry edges together to seal. Repeat with remaining sausages and puff pastry.
Brush the pastry with whisked egg yolk.
Cook in the oven for 30 minutes. Remove from oven and cool for 5 minutes before serving.