Premise 1: Butter goes good with toast.
Premise 2: Toast goes along with coffee.
Conclusion: Butter goes good in coffee.
I wrote a while ago about an experiment in which I tried peanut butter in some coffee. It turned out pretty well. I've since tried it with all-natural peanut butter, with similar results (I still haven't solved the sludge- on- the- bottom problem though). So I figure, why not get rid of the peanuts and try it with pure butter? Note: I usually think of things like this when V is at work, and thus not around to tell me not to do stupid things.
I Googled "butter in coffee" first, to see if this is commonly done and/or if any poisonous chemical reactions would take place. I found this dude, who was apparently emboldened to try peanut butter in his coffee after seeing my last experiment's post. He liked it too. Nice. But apparently butter, minus the peanut, is not commonly put in coffee (though I found one recipe, linked below).
Being brave and manly, I went on and did it anyway. I put just a bit of butter - I'd say a teaspoon or so - in a mug, added sweetener (wouldn't want to drink anything unhealthy!), poured some hot chocolate-tinted coffee over it, then added cream. It took a moment to melt, then left a bit of an oily film on the coffee. Weird.
How did it taste? Good, of course. The butter gave the beverage an added richness. With the chocolate also in the coffee, I would describe it like drinking a chocolate chip cookie. With coffee. In fact, I'll call this recipe "chocolate chip cookie coffee". That's copyright 2007, me, so if you use it you have to pay me lots of money. Thanks.
I'll let you have a free trial though, and I do recommend trying it. Unlike the peanut butter coffee, there is no gross sludge to worry about, and it seriously does taste good. And come on, a teaspoon of butter won't clog your arteries too much.
See also: Food Logic Volume 2: Peanut butter coffee.
Also see also: Hot buttered Jamaican coffee.