This contest calls for butter, but does not specify what kind. These days, there are good vegan butters available (for those who may scoff and deride them as mere margarine: not necessarily so). And vegans do enjoy buttery things -- even if not dairy.
Back in the day, some time during the Pleistocene Age, I used to make a dairy version of this fudge. Wanting to make this for the vegans in my life, I fiddled around with ingredients and proportions till I got it right. It's really easy to make, and especially nice to have for the holidays.
Combine brown sugar, milk and butter in a pot. Bring to a full boil, over medium-low heat, stirring occasionally. Pour over confectioner's sugar and beat (I use a stand mixer but a mixer or beating by hand works), add vanilla, and beat thoroughly till smooth. Pour into a greased 8" pan. Refrigerate to store.