I’ve never heard of butter in coffee. I’d have to try it before judgement. After being in the Navy, you learn all kinds of ways to “ flavor coffee. Such as not changing the grounds for at least a week, just add a little new. Salt, eggshells might be the worst one I remember. Took me a few years to start drinking coffee again after getting out. I have the Kuerig system that the wife uses but prefer paper filter with fresh ground. The best I have ever had is fresh roasted, rested for an hour to degas then brewed. I even have a one batch roaster. You can use a frying pan to roast but be prepared for the smell and skins coming off the beans while roasting. Momma bear won’t like it.