Yule Bannock was a bannock that was made round with notched edges.
The dough was made from finely-ground oatmeal.
After the arrival of Christianity, the bannock came to be marked on the top with a cross, dividing it into four. The tradition was to bake them early on Christmas Day, one for each person who’d be there as a present. They had to stow it somewhere where it wouldn’t break or get nibbled on, either by themselves or a household animal until Christmas dinner. If kept intact until then, it meant good luck.
For serving, it wasn’t cut into wedges, but rather broken into pieces.
Contemporary speculation is that the notches were meant to represent the sun’s rays, dating these bannock back to pagan worship. Others say that this may be a modern interpretation made by writers who’ve seen too many Mayan souvenir sun carvings. The notches in fact weren’t great triangle-shaped hunks cut out of the side.
More usually, the notches were just done between your thumb and finger, as your Aunt Bessie would do any day of the week on a pie crust without being accused of heathen ways. The notches would have served the purpose of both making the bannock look fancier for the occasion, and help stop the edges from crumbling.