This is a “leftover” soup. After a traditional meal of Haggis with mashed potato and mashed turnip, you may have a load of leftovers, through the whole lot in a pan and add some liquid (water will do as the haggis has enough flavour any way), bring to the boil and using a whisk or stick blender combine all the ingredients until smooth. You won’t be able to get it perfectly smooth becasuse of the oats in the haggis but there should be no big lumps and the three ingrediants should be completely combined.
Ideally the proportions of the three ingredients should be roughly equivalent to the portions you would serve for dinner. So if you have three portions of haggis, you would use three portions of mash and three of neeps.
This soup doesn’t look that appetising, but it is delicious.