Simply toss the liver slices in flour seasoned with salt and pepper, then lay them into the slow cooker along with the sliced onions and a couple of knobs of butter.
Mix the stock with Worcestershire sauce and sage, then pour this over the liver and onions, giving everything a gentle stir to combine.
Cover and cook on low for 8 hours until the liver is tender and the onions have turned soft and sweet.
Serve hot with creamy mashed potato, spooning over the rich, savoury gravy.
