To make the pastry
Combine the butter, flour and salt, then add just enough water to bring it together into a dough.
Form into a rectangular shape with your hands and on a well-floured surface, roll out in one direction, away from you, so you have a rectangle about one centimetre thick. Fold the two short ends into the middle so they overlap. Give the pastry a quarter turn, and repeat the rolling-and-folding process five more times.
Wrap the pastry in clingfilm, then rest it in the fridge for 30 minutes to an hour.
To make the filling
Heat the oven to 180C/Gas mark 6.
Season the beef and kidney pieces then toss them in the flour, shaking off any excess.
Set a large heavy based pan over a low/medium heat. Add half the dripping and once hot add the steak and kidney pieces. Brown well on all sides then lift it out to a plate and set to once side. You’ll need to do this in batches.
Add the remaining dripping to the pan followed by the sliced onions and garlic. Season with salt and pepper and cook for 10 – 12 minutes or until soft and fragrant. Return the meat to the pan, along with the thyme and bay leaves. Pour in the ale and the stock and bring to a simmer. Add the Worcester sauce and mustard and stir everything well.
Cover (with the lid ajar) and place in the preheated oven for 1 ½ - 2 hours hours or until the meat is tender and the sauce thickened. If it looks a little dry at any point add a splash of water to loosen it up again. Let the pie filling cool once it’s ready.
To make the pie
Cut the pastry into two pieces of two-thirds and one-third. Roll out the larger piece and line a lightly greased pie dish (about 1.2 litres). Don’t worry if you have some overhang, this gets trimmed off.
Spoon in the steak and kidney pie filling, but remove the bay leaves and herb stalks.
Roll out the smaller piece of pastry to form a lid.
Brush the edges of the pastry base with some egg wash, lay on the lid and crimp together the edges. Trim away any excess pastry. Brush with more egg, and cut a vent in the centre of the pie.
Bake for 45-50 minutes, or until golden brown.
Leave to cool for 15 minutes, then serve with mash, greens and English mustard.