Heat a 12" cast iron skillet over high heat. Lower heat to medium, and working in 2 batches, add beans, and cook, stirring, until toasted and beginning to pop, about for 10 minutes. Remove cacao beans from heat ,and transfer to a bowl; set aside to cool.
Using a manual grinder, pass the warm, toasted cacao beans through the grinder onto a clean work surface until they become a smooth paste, about 3 times. Transfer the cacao paste to a bowl. Add sugar, cinnamon, and vanilla, and mix well by hand. The mixture will have a crumbly texture. Pass this chocolate mixture one last time through the grinder.
Place the ring mold on a clean, sturdy surface. Scoop about 1 cup of chocolate mixture into the ring and pack it in using your fingers. To ensure a tightly-packed tablet, use the bottom of a heavy skillet and pound it against the top of the ring. Continue adding the mixture and pounding until you have a smooth, even surface.
Using a sharp knife, make an incision at the diameter across the surface of the tablet, about ¾" deep; remove mold and let tablet cool to harden. Wrap tablets individually in plastic wrap or parchment paper. Store in an airtight container at room temperature for 3 to 4 months or in the refrigerator for 6 months to 1 year.