My love is like a red red sheep's offal

I do love a McSween, split open and packed into a baking tray, a layer of chopped spring onion or leek, covered with a layer of mustard mashed potato. Stuck in the oven and towards the end, grilled with a sprinkling of cheddar.

I still remember at school being caught out by a question; what was the largest island before Australia was discovered?