Heat the oil in a large non stick pan on medium high heat, when hot, brown the beef on all sides, work in batches if needed, not trying to cook through, just get most of it browned. Remove the beef and set aside.
Same pan, add the kidney and brown on all sides, again, not trying to cook through, just brown it.
When the kidney is browned, add the onion to the pan and saute for 3-4 minutes until the onion is soft.
Return the beef to the pan and mix everything together, then sprinkle the flour in and stir to coat everything with flour.
Pour in the beef stock and stir together, bring the heat to a boil then reduce to a simmer. Simmer uncovered for 1½ hours, stirring occasionally, If the liquid reduces to much, add stock as needed.
Remove from heat, season with salt, pepper, and Worcestershire sauce as desired, stirring in and tasting. Set this aside and allow to cool completely.
Preheat your oven to 220° C (425° F). Get out a pie dish.
When the meat mixture has completely cooled, pour it into the pie dish.
Roll out the puff pastry to just under 1/4 inch thick, use the rolling pin and transfer to the pie dish and cover the top and flute the edge. Brush the top with the beaten egg.
Bake for 30-40 minutes or until the top is golden brown brown and puffed.
Serve with mashed potatoes and vegetables for a complete, and filling meal.