A little dab of butter can do interesting things to an espresso shot. It seems to bring out the flavor rather than cover it up like milk or cream does. The other effect is that the butter slows the absorption of caffeine so the lift is a gentle sustained experience rather than the roller coaster you get from knocking down a double shot. If you decide to try this at an espresso bar be sure to insist on salt free butter. I made the mistake of asking for butter at an espresso bar in Seattle and not specifying, ended up with the salted variety....... yecchh, but I drank it anyway. Don't be that guy!!!