Add 1 inch of water into the bottom of a pot. Place a glass bowl on top to create a double boiler.
Bring the pot to a simmer, then turn the heat down to medium-low.
Add the cocoa butter into the bowl to melt. It takes about 5 minutes to fully melt.
Whisk in the cocoa powder, agave or maple syrup, vanilla, and salt until fully incorporated. Be careful not to spill the hot chocolate. Wear an oven mitt to hold onto the bowl and stabilize it.
Remove from the heat.
Pour into molds and then let the chocolate set, either on the counter at room temperature or in the fridge. It takes 1-2 hours to set in the fridge.
This recipe makes about 3 of the chocolate bar molds. Alternatively, if you fill muffin cups about 1/3 of the way you can make about 12 chocolate cups - this is what the serving size and nutrition facts are based on.