Chocolate (from the nahuatl Xocolatl) was an energetic beverage only for the royalty in prehispanic Mexico. It was a mix of grounded seeds of cacao mixed with chillies and salt. When the Spanish tried it, they found the strong taste unbearable, so they added sugar instead of chillies and salt. They started to make it in blocks and sent it to Europe in the XVI century, where it slowly became very popular, first with the royal class, the aristocrats and wealthy people. The chocolate rooms were very popular among the rich and powerful, adding new flavours, like cinnamon and the also Mexican vanilla. Over time, its consumption was extended to the rest of the population and now it is a very popular treat at an affordable price. In Mexico, the way to drink it was dissolving a tablet of chocolate in 1L of boiling water or milk, and stirring with with an artisan wooden stirrer to make it foamy and drink it usually with the family during the evening. It's perfect in celebrations like Day of the Dead and the Rosca de Reyes in January.
Keep in a cool, dry place, away from sun and humidity.