I don't know how well-known haslet is throughout the UK (and indeed the world), but it deserves to be very popular. Made from minced pork and offal, it's a deliciously savoury meaty loaf that's perfect eaten cold with a salad or sliced in a sandwich.
If you are using pork belly, you'll need to cut the rind off. Cut the liver and the belly pork into chunks small enough to go through a mincer. Peel and quarter the onion. Fit the medium plate to the mincer and feed the liver, pork and onion through, alternating the items now and again. If you don't have a mincer, cut the liver and onion as finely as you can. Make up the seasoning mix in a small screw-top jar and give it a really good shake. Finely chop the sage leaves, if using, and mix those in with the seasoning. Add 3 teaspoons of seasoning and a beaten egg to the meat mixture, squeeze the softened bread to get the milk out of it and mix it thoroughly with everything else.
Heat your oven to 160° Celsius (320° Fahrenheit) for a fan/convection/airfryer oven, or 180° Celsius (356° Fahrenheit) for a conventional one, or gas 4.
Place the haslet in the fridge to cool right down. Serve sliced haslet with a salad or in sandwiches. It's not usually eaten hot, but if you slice it and fry it, it goes very well with a full English breakfast.
Seasoning mix for haslet: 4 parts salt, 1 part white pepper, 1 part ground black pepper, 2 parts dried sage, 1 part mace, 1 part allspice.