When you are making a chocolate brulee or any kind of chocolate anglaise, achieving a completely smooth texture in the final product can be tricky, but there is a way to do it.
The trick is to half melt your chocolate; essentially meaning that some of your chocolate is melted, but there are still some lumps of unmelted, but hot chocolate. Half melting will heat your chocolate up enough that it will melt completely when your cream is added but still leep some of the stable cocoa butter crystals needed to make a perfect emulsion.
If you fully melt your chocolate, there are no tempered cocoa butter crystals left to remain stable, and that can affect the texture of the final product. If totally unmelted your chocolate may not fully melt out with the heat of the liquid and might require further heating to do so, which greatly increases the risk of scalding, burning and curdling.
With your chocolate half melted, take 1/3 of your hot liquid (for an angliase, this can be done before or after re-cooking as long as it is still warm enough to melt the chocolate the rest of the way), and pour it over all the chocolate. Let it sit for about a minute, and then with your immersion blender, tying not to incorporate any air, emulsify your mixture.
It will be tricky and depending on the ratio of liquid to chocolate, tough on your blender, but do what you can before adding the next 1/3. Repeat the process and you should be left with a totally smooth emulsion ready to be baked or served.