When you say you used a 2:1 ratio of cocoa butter to cocoa powder do you mean by weight? That seems like a very large amount of cocoa butter, much more than is typical. I think it should be more like 1:1 ratio. I think you'll get better results by doing like I was doing and using unsweetened chocolate as your starting point. Note that with the formula I followed posted above I did not notice a cooling effect from the erythritol---there isn't enough erythritol to cause that problem. However, the chocolate is not super-sweet like everybody making sugar-free chocolate seems to prefer. Note that I did not have problems with "clumping" but with the mouth feel of the chocolate being coarse textured.
I think the reason your chocolate melts quickly is that you didn't temper it. Lately I've been tempering using Mycryo but if you don't want to go that route the easiest way is to add tempered chocolate as a seed to control crystallization of the cocoa butter.
