Risalamande was invented when the rice was easy to get, so the upper class had to serve something more “expensive”, than what the common people eat Christmas eve.
Wondering about the one whole almond ? the rule is, the one there get the almond, get a little present. The almond goes in the pot with Risalamande and the person who have the almond can reveal himself when the whole pot of Risalamande. You can also just put it in a random plate, switch the all the plates a couple of times so you do know where it is - Enjoy.