A buddy of mine (sarge27) said he read somewhere that adding some vanilla extract to a bottle of Velvet Merlin was supposed to be good. I'm sure this isn't an exact science since it depends on individual palates but I added 1/8 tsp vanilla extract to a bottle that I had poured into a snifter and it was fantastic. A little something fun to try. I know there's a lot of people who like it as it is but having had Velvet Merkin recently, I found Merlin lacking and was looking for more. This did it for me.
I was a big fan of Stone Smoked porter with Vanilla Bean but they barely ever made it so a few years ago I experimented with adding a couple drops of vanilla extract to Black Butte Porter... was pretty good.
