MAKE THE SHORTCRUST PASTRY:
In a large bowl, combine flour and salt.
Add cold butter and lard, using a pastry cutter or fingertips to rub into flour until mixture resembles coarse breadcrumbs.
Add ice water 1 tablespoon at a time, mixing with a fork until dough just comes together.
Turn out onto work surface and gently press into a cohesive dough (don't overwork).
Divide into two portions (one slightly larger for bottom crust).
Flatten each into a disk, wrap in plastic wrap.
Refrigerate for at least 1 hour, preferably 2 hours.

PREPARE THE CLOVE-STUDDED ONION:
Rob's traditional touch: Stud the whole peeled onion with cloves, pushing them into the onion at regular intervals.
This will infuse the filling with warm aromatic spice.

MAKE THE CHICKEN AND MUSHROOM FILLING:
In a large pot or Dutch oven, melt 2 tablespoons butter over medium-high heat.
Season chicken pieces with salt and pepper.
Brown chicken pieces lightly on all sides, just 3-4 minutes total - they will finish cooking in the oven. Remove and set aside.
In the same pot, melt remaining 2 tablespoons butter.
Add sliced mushrooms and cook until browned and liquid has evaporated, about 8-10 minutes.
Add diced carrots and celery, cook for 5 minutes until slightly softened.
Sprinkle flour over vegetables and stir for 1-2 minutes.
Gradually add chicken stock, stirring constantly to prevent lumps.
Add the clove-studded onion, thyme, and bay leaves.
Bring to a simmer and cook for 15-20 minutes until vegetables are tender and sauce has thickened.
Remove clove-studded onion and bay leaves. Discard onion or reserve for another use.
Stir in cream and return lightly browned chicken to the pot.
Add parsley and season generously with salt and pepper.
Let filling cool completely before assembling pie - hot filling will make pastry soggy.

ASSEMBLE THE PIE:
Preheat oven to 400°F. Place a baking sheet in the oven to preheat (this helps crisp the bottom).
On a lightly floured surface, roll out the larger pastry disk to fit a 9-inch deep pie dish with overhang.
Line pie dish with pastry, letting excess hang over edges.
Pour cooled chicken and mushroom filling into pastry-lined dish.
Roll out second pastry disk for the top crust.
Brush edges of bottom crust with beaten egg.
Place top crust over filling, pressing edges together to seal.
Trim excess pastry and crimp edges decoratively.
Cut several slits in the top to allow steam to escape.
Brush entire top with beaten egg wash.
As a Lancashire-born baker, pie making is one of Rob's specialties - traditional decoration like crimped edges is typical.

BAKE:
Place pie on preheated baking sheet in oven.
Bake for 20 minutes at 400°F.
Reduce temperature to 350°F and continue baking for 35-40 minutes until pastry is deep golden brown and filling is bubbling through the vents. Visually it should have a nice color.
If edges brown too quickly, cover with foil.
Let rest for 15 minutes before slicing.