How to harden a chocolate made from Regular (unsalted) butter?
This cannot be done. Chocolate has the hardness of chocolate, because it is made out of cocoa butter. Dairy butter is not suitable for that. There are industrial processes which use hydrogenated plant fat and emulsifiers to make chocolate bars with a somewhat different texture than pure chocolate, but still hard - I doubt that you can do that without industrial grade equipment. 

For all practical purposes, what you are trying to do is impossible.