First, melt your chocolate, and then bring cream to a full boil, taking it off the stove as soon as it has reached that point. Then, let it cool a bit and pour it incrementally into the warm (but not too hot!) melted chocolate, making sure to stir it well—you want it to be all incorporated before you hand-blend it. Once you're ready to hand-blend, start with the blender (not yet turned on) in the middle of the liquid and turn it on to medium speed, rotating the bowl a few times as you hold the blender steady. After 15 seconds or so, stop the blender, use a spatula to scrape down the sides of the bowl, and start blending again on high speed.