I make this one in an 8 x 8 baking dish lined with parchment. It is firm in a few minutes, and I remove it (using the parchment as handles), cut it into squares, stick it in a plastic ware container, label it, and pop it in the freezer. That is how I distinguish this from the Milk Chocolate Bars, which I make in molds.
Also, see instructions for making powdered sugar-free sweetener
here. Note that this can be made with granulated sweetener, but would have to be mixed in a food processor in that case.