Start making about 2 hours before planning to serve
If using mushrooms, clean and quarter them. Fry in a little oil until slightly browned and all their water evaporated. Remove to a bowl.
Chop the bacon in small chunks and start frying it. Clean and slice the leek and add it to the bacon and continue frying. Cover if needed.
Peel and finely slice the carrots and add to the bacon and leek. Add also the celery.
Cut the chicken into cubes and add the pan. Cook until it doesn’t look raw on the outside. Season with salt, pepper, Worcestershire and 1-2 tsp of Dijon mustard.
Sprinkle over some flour, mix to combine, then add enough stock to make a sauce. Add in the mushrooms, if using, and the green peas. Give it a final mix to combine then place in the pie dish.
Cover with puff pastry, poke a few holes in it and bake at 200 C until done.
While the pie is baking, make some mashed potatoes. When the pie is almost done, boil also the peas then stir with a bit of butter and salt and pepper.
Serve the pie with mashed potatoes, peas and beer.