It really is so much better to make the stew the day before for two reasons. The first is the flavors get so much better as the stew marinades over night and the second is, it allows you to remove any fat that has settled at the top of the stew.
Begin by covering all the beef well in flour along with plenty of seasoning. In a hot pan drizzle a little oil and add half the butter along with the beef, turning all the time. Continue to fry the beef until it takes on a rich brown colour, remove from the pan and set aside.
Now, in the same pan add a little more oil and remaining butter along with the kidneys, portobello mushroom and thyme, fry until golden and set aside with the beef. Return the pan to the heat and add the onion and carrots, frying just for 4-5 minutes. Now add the red wine to the pan along with the porcini mushrooms, their soaking liquor, the balsamic vinegar and worchester sauce.
Allow this to reduce by half, stirring all the time to ensure all the residue on the pan becomes incorporated in the sauce.
Now place the contents of the pan in a large pot along with the beef and mushroom. Add the stock and bay leaves.
Simmer for about 45 minutes or until the beef becomes soft and tender. Allow to cool and refrigerate over night
On the day of serving, line a well greased pie dish with puff pastry leaving a little hanging over the edge, allowing for shrinkage.
Remove any excess fat from the top of the stew before reheating. Heat the pie filling gently in a large pot, there is no need to over heat as it will heat further in the oven. Now fill your pie dish to the top using a slotted spoon so as not to put too much juice in (retain any excess).
Now cover with puff pastry again allowing a little for shrinkage and brush with egg wash.
Use a sharp knife to crate a hole in the centre of the pie to allow the steam to escape. You can use the excess pastry to create a design on top of the pie, maybe a few leaves.
Bake the pie in a pre heated oven at 160 degrees for about 40 minutes. All ovens vary and so you should take care not to have the oven too hot!!
Place any remaining juices into a pot to boil while the pie is cooking and reduce to a sauce consistency ready to pore over the pie when you serve! Enjoy!