I like using dark chocolate in fudge. It contrasts nicely with the coffee flavor of the Kahlua and it’s not overly sweet. But not everyone shares my obsession with dark chocolate.  You can make your Kahlua chocolate fudge with the chocolate of your choice. Substitute semi-sweet chocolate or white chocolate if you really want to highlight the Kahlua. Just use less of the espresso powder (or leave it out altogether). The lighter you go, the sweeter your Kahlua Fudge will be.