Directions

1. First make the pastry (it's best if it rests). Put the flour, mustard powder, some flaky sea salt and the lard and/or butter in a food processor and pulse until the texture of breadcrumbs. Add half the egg and pulse again. Add a few tbsp cold water, if needed, until it forms a short pastry. Knead quickly into a ball and chill in the fridge. Can be made 2 days ahead or frozen for 1 month.
2. Heat oven to 160C/140C fan/gas 3. Mix the flour with the mustard powder and cayenne pepper, then coat the beef chunks and kidneys in the flour - keeping them separate. Heat the oil in a large flameproof casserole and brown the beef chunks in batches. Set aside, then brown the kidneys and tip into a colander to drain. In the same pan, sizzle the bacon and add the carrots, onions and bay, and cook until browned. Pour over the ale, stock and tomato puree, then reduce quickly, scraping the base of the dish.
3. Return the beef chunks to the dish, nestle the thyme into the mix, then season. Cover and braise in the oven for 2 hrs, stirring the kidneys into the stew halfway through. Can now be kept in the fridge for up to 2 days, or frozen for 1 month.
4. Heat oven to 220C/200C fan/gas 7. To make the pie, tip the stew into a baking dish or shallow casserole. Place a piece of bone marrow in the middle, if using; if not, an upturned egg cup will do the same job. Roll out the pastry to fit the dish with enough to overhang, then drape over the stew, seal the edges and cut off the excess. Use trimmings to make leaves to decorate. Brush the pastry all over with the remaining egg, sprinkle with flaky sea salt and bake for 40 mins until golden. Leave to rest for 10 mins, then serve the pie with teaspoons for the bone marrow, for those who want it.