Sift flour into a bowl, rub in butter and salt until the mixture looks like breadcrumbs.
Add ice-cold water gradually, mix into a dough, wrap, and chill for 20 minutes.
Roll dough to a 40cm x 20cm rectangle, fold into thirds, turn, roll again, then chill for 30 minutes.
Repeat the rolling and folding process twice more, then chill until needed.
Marinate beef with garlic, thyme, peppercorns, and ale for at least 3 hours.
Pat beef dry, dredge in seasoned flour, and strain the marinade into a bowl for later use.
Brown the beef in oil and 15g butter in batches, then set aside.
Fry mushrooms and shallots in the same dish for 5 minutes until softened.
Combine beef, marinade, and stock, then simmer covered for 90 minutes until tender.
Strain half the liquid and reserve it for gravy.
Melt Stilton into the filling, season, and let cool.
Preheat oven to 180°C and flour four 10cm rings on a baking tray.
Fill the rings with the cooled beef and Stilton mixture.
Roll pastry to 2.5cm thickness and cut four circles to cover the rings.
Seal pastry lids with egg wash, crimp edges, vent the centers, and glaze with remaining egg.
Bake for 20 minutes until the pastry is golden and crisp.
Reduce reserved cooking liquid to gravy consistency and whisk in 15g butter.
Boil celeriac and potatoes separately until tender, then drain and dry over heat.
Mash them with butter, cream, and mustard, then season.
Preheat oven to 220°C for the beetroot.
Mix thyme, vinegar, oil, and honey in a bowl.
Scoop beetroot into balls and toss in the honey mixture with seasoning.
Roast beetroot for 15 minutes until sticky and glazed.
Serve the pies with mash, roasted beetroot, and warm gravy.