Season the brisket all over with salt and pepper. Heat the vegetable oil in a frying pan (or use the sear function on your slow cooker) and sear the meat all over until browned. Transfer to a plate. Add another drizzle of oil, if needed, and fry the onions with a pinch of salt until lightly golden, about 12 mins. Sprinkle over the flour, stir until well-mixed, then pour in the ale and scrape the bottom of the pan to pick up any browned bits. Tip everything into the slow cooker (if using a frying pan).

Add the yeast or beef extract, sugar and vinegar, then the beef and herbs. Top up with stock until the brisket is just over half submerged. Cover and cook for 7-8 hrs on low until tender. Remove the meat from the slow cooker and cover to keep warm. Use the reduce or simmer function on your slow cooker and simmer for 10-15 mins until the gravy has thickened to your liking. If your slow cooker doesn’t have a simmer function, pour the gravy into a pan and simmer on the hob until thickened. Add a pinch more salt, sugar or a dash more vinegar if needed. If you like your gravy to be extra-thick, mix the cornflour with a splash of cold water, then add to the pan and bubble for a few minutes.

Just before you remove the meat from the slow cooker, start on the mash. Cook the potatoes in a pan of boiling salted water for 20 mins until very tender when pressed. Drain and steam-dry for a few minutes before mashing with the horseradish, butter and crème fraîche. Scatter with parsley to serve. Cut the brisket into wedges and serve with the gravy and mash.