Trim and cut the Beef Chuck into 2–3 cm cubes; trim, halve and remove any core or sinew from the Lamb Kidneys and slice them into bite‑size pieces. Peel and roughly chop the Onion.
Season the meat and kidneys with Salt and freshly ground Black Pepper.
Heat a large heavy‑based pan with a little Vegetable Oil over high heat. In batches, brown the beef cubes well on all sides, transferring them to a plate as they colour to avoid steaming.
Reduce the heat, add a touch more oil if needed and soften the chopped onion in the same pan until translucent and starting to colour.
Stir in the Plain Flour and cook for 1–2 minutes to remove the raw flour taste and help thicken the sauce.
Pour in the Dark Ale to deglaze the pan, scraping up any browned bits, then add the Beef Stock, a splash of Worcestershire Sauce, the Bay Leaf and the Thyme. Return the browned beef to the pan.
Bring to a simmer, cover and cook gently for about 1 to 1½ hours until the beef is nearly tender. Add the sliced kidneys for the last 20–30 minutes of cooking so they stay tender but lose any strong flavour.
Once the meat is tender, remove the lid and reduce the sauce over medium heat until it is thick and glossy. Taste and adjust seasoning with more Salt and Black Pepper if needed. Remove and discard the bay leaf and any thyme stalks, then cool the filling slightly.
Make the hot‑water crust pastry: in a small saucepan heat the Water with the Unsalted Butter and Lard until the fats have just melted and the mixture is hot. Put the Plain Flour and a pinch of Salt in a bowl, pour the hot fat mixture over it, and stir quickly to form a dough. When cool enough to handle, knead briefly until smooth.
Divide the pastry into a larger piece for lining the tin and a smaller piece for the lid. Roll out the larger piece and line a 20–23 cm pie tin, leaving a slight overhang. Fill with the cooled meat mixture, then seal with the rolled lid, crimping the edges to secure and cutting a small steam hole in the centre.
Beat the Egg and brush it over the pastry for a shiny, golden finish. Bake in a preheated oven at 200°C (400°F) for 35–45 minutes, or until the crust is deeply golden and the filling is bubbling. Allow the pie to rest for 10–15 minutes before serving.
