Béaltaine Bannock was a form of bread.
There were various traditions and forms of it being made up until the end of the 1800s.
It was a bannock that was usually round, though sometimes it was triangular. While making it, no metal implements were to be used. Some traditions held that the bannock dough had to be kneaded in your hand — e.g. not on a surface, as you normally would.
When cooked, it was washed with Béaltaine Caudle, as a sort of batter, then put back on the griddle to toast the batter until it was brown on both sides, then dipped again in the caudle and browned again, repeating the process until a good layer of batter was built up.
Another version of Béaltaine Bannock was a bannock with nine raised knobs or balls on it. You would take your bannock, stand looking at the fire, break off a piece, and toss it backwards over your shoulder, saying which spirit you were giving it to. Nine knobs allowed you to cover many bases. You could even cover animals, such as the fox who might harm your chickens.
In some places in Wales, Béaltaine fires would be lit. Two types of bannock would be made, one type from oatmeal and another type from a brown meal, probably barley. Each bannock would be cut into four, and the pieces put into a bag together. Those who picked the oatmeal pieces out of the bag were lucky; they just had to sing and dance. Those who got the brown meal pieces had to run in between the fires, or jump over the fires three times. Jumping over or running through fires was supposed to bring a good harvest.
On the Isle of Mull, off the west coast of Scotland, some people would make a very large bannock with a hole in the centre. The aim was to milk the cows, aiming the milk through the hole. This reputedly brought good luck.
Other Béaltaine Bannocks were left on the doorsteps for the Fairies that night, in the hopes that they’d look favourably upon your house.
In some parts of the UK, one side of the Béaltaine Bannock would have a mark on it that meant ill luck or even death. You’d roll your bannock down a hill, and hope that the bad side didn’t come up. It was also bad luck if your bannock broke on you during the rolling.
In other Béaltaine Bannock traditions, a bannock would be cooked then broken up into pieces. One piece would be blackened with ash, and put into a bag, for people to choose pieces from, blindfolded. A variant version had a bunch of small bannocks made, with one of them blackened with soot.
Whoever ended up with the blackened bannock had the honour of being the “Béaltaine Carline” (“cailleach béaltaine” in Gaelic), which meant the Béaltaine sacrificial offering. This person would be the symbolic scapegoat, upon whom the misfortune stored up for the village in the coming year would all fall. This meant various things, depending upon geography and time in history, and it wasn’t always just symbolic.
In enlightened communities, the person with the blackened piece just had to jump through the fire three times to purify himself of the misfortune that he’d taken on. If he didn’t, the bad luck he had assumed for the others would stick with him until Béaltaine next year.
In 1984, however, near Manchester, England, the corpse of a man now referred to as the “Lindow Man” was found, preserved by the peat bog. He appeared to have been murdered quite deliberately — killed three different ways in fact, sometime between A.D. 50 and A.D. 100. Examiners found about 1 oz (30 g) of food in his stomach, that were wheat, bran and barley grains, some of them burnt. From this comes speculation that it was a piece of burnt Béaltaine Bannock cake in his stomach. Also in his stomach was mistletoe pollen, which can act as a sedative or narcotic. This has led some Archaeologists to speculate that he was a Béaltaine sacrifice. 
The Béaltaine sacrifice being killed three different ways, however, would have been unusual. Generally the person was just burnt in the fire.
Over time, as other traditions faded and people forgot their “pagan past”, a Béaltaine Bannock could be made with a cross scored on one side of the bannock and a circle on the other.
 Others say the Lindow Man was just the victim of a very gruesome murder, or that he could even have just been trampled by a horse, and that none of the “sacrifice” evidence would stand up in a court. He is on display at the British Museum.
In Scottish, it was called “Bonnach Béaltaine.”