At home in Scotland as a boy we had "mutton" pies reheated in the oven then we covered the top with tomato ketchup before cutting into the hot spicy centre.

We called then "mutton" pies (or just pies) but I always thought that there was very little meat therein (this was wartime and the depressing post-war 40s and 50s). I was sure it was just spicy porridge with some probably unmentionable bits of lamb but it tasted good. So does haggis and it has the same basis.