The cookies themselves are perfectly rich and chewy, which is pretty much a requirement in my mind, and the ganache is silky and luscious with that little bite of Kahlua and a peppermint zing.
In the bowl of a stand mixer fitted with the paddle attachment (or using a bowl and handheld electric mixer), cream together the butter and sugars until pale and fluffy.
Wipe down bowl/beater and sift the dry ingredients into the wet. Mix in on lowest speed until all ingredients are almost evenly combined, and then finish folding in with a spatula.
Divide dough in half and shape each half into a small, flat square on a piece of plastic wrap. Wrap and refrigerate for 1 ½ - 2 hours, until cold and firm.