First, rinse the sheep's stomach thoroughly and soak it overnight in cold saltwater.
Rinse the sheep's liver, heart and tongue. In a large pot with boiling water, cook these in salted water for 2 hours over medium flame. Remove and mince and remove any extra skins and discard them.
Take a large bowl, combine the liver, heart, tongue, suet, onions and oats. Mix all of them properly. Season it with salt, pepper and herbs. Remove the stomach from cold water and fill 2/3rd of the mixture. Then tie the stomach closed with the mixture inside it. This will prevent the dish from bursting.
Take a large pot with boiling water and gently place the stomach in it without splashing the mixture in it. Cook it for over 3 hours. The haggis is ready.
Take a small bowl, mash some boiled potatoes with salt seasoning and serve it with the haggis.