Haggis!

 In every country, there's a strange need to make up stuff for the unwary foreigner. In Scotland it's the Wild Haggis!
 Haggis is sheeps heart and liver and lungs wrapped in spices and oatmeal and its stomach, and then boiled. Personally I don't like the taste, but it's the food most associated with Scotland, and traditionally it gets served on Burns night.
 Is Haggis Scottish? Certainly, we've taken it as our own. However, like everything else it has a complicated history.

The use and vertues of these two severall kinds of Oate-meales in maintaining the Family, they are so many (according to the many customes of many Nations) that it is almost impossible to recken all;” and then proceeds to give a description of “oat-meale mixed with blood, and the Liver of either Sheepe, Calfe or Swine, maketh that pudding which is called the Haggas or Haggus, of whose goodnesse it is in vaine to boast, because there is hardly to be found a man that doth not affect them

— Gervase Markham, The English Huswife (1615), England.

Which is pretty early. But...

Thy fowll front had, and he that Bartilmo flaid; The gallowis gaipis eftir thy graceles gruntill, As thow wald for ane haggeis, hungry gled.

— William Dunbar, Flyting of Dunbar and Kennedy (circa 1520), Scotland.

So, we're still in the lead (so to speak). But...

For hagese'.

Þe hert of schepe, þe nere þou take,

Þo bowel noght þou shalle forsake,

On þe turbilen made, and boyled wele,

Hacke alle togeder with gode persole,

                                          — Liber Cure Cocorum, circa 1430, England.

 From all this, it's impossible to say who actually invented Haggis. England and Scotland are neighbours, so historically it's easy enough for ideas to be transmitted frequently between the two. Haggis is a food that pretty much uses the whole of the ship in as efficient a manner as possible. It would be strange if haggis hadn't evolved independently amongst agricultural peoples over the whole of human history. Just like porridge, a high-energy food that's incredibly easy to produce.
 So, historians have argued that haggis is in fact much, much, older than England or Scotland. It's been argued that the ancient romans were aware of it, that the Scandanavians brought it over in their longboats, that it was even referenced in Homers The Odyssey. I think there probably is a grain of truth in this. Food evolves, ideas evolve. Rarely in human history does an idea spring forth without antecendant. Haggis is Scottish, inasmuch as we still eat it and it's culturally associated with us, but at the same time it almost certainly has wider historical implications.