Start with chocolate chips in a double boiler - or a heat safe bowl over simmering water:
When it's melted, remove from the heat and add in a handful of room-temp chips. This tempers the chocolate. Otherwise it won't set - it'll be mushy at room temperature.
Stir until completely smooth and place into a piping (or ziptop) bag. Using a small opening tip (or cut a small hole in the bag) drizzle the chocolate into an oiled container. I used a fluted ramekin.
You can speed up the setting process by freezing it. Then gently remove it from the container.