Try this great and unusual cake made with root beer. You can find root beer essence in some supermarkets.
This was better and moister than one I made from Food Network. I actually baked them in 12oz glass rootbeer mugs and made a simple frosting from Dream Whip and 1/2 c. rootbeer. For decoration, I stuck a straw in. I will make this again. - 09 Aug 2004 (Review from Allrecipes USA and Canada)
I made cupcakes with this recipe using Milwaukee's own Sprecher root beer and was thrilled with them right up until I took the first bite. In my judgement they are in flavor and crumb more like a basic muffin (the non-cake type). Not moist enough for my liking, nor are they sweet enough. Their saving grace is the frosting, which is to-die-for good, but even then I tinkered with the recipe because it wouldn't have worked for me as written. Since I piped the frosting and needed it to be stiffer, I used a little more powdered sugar than called for and considerably less root beer. At least this awesome frosting picked up the slack for the lifeless cupcakes. They were pretty, no doubt about it, with their swirls of delicately caramel-colored frosting and bits of crushed root beer barrels I sprinkled them with as garnish, but being pretty isn't enough. I am still looking to make a great root beer cake so if I was to use this recipe again I'd probably add another egg, maybe even two, and another 1/2 cup sugar. - 12 Jan 2010 (Review from Allrecipes USA and Canada)
this was good, I couldn't find the root beer extract, so i just put in more root beer. I used canned vanilla icing w/root beer mixed in, which turned out very good as well - 15 Mar 2008 (Review from Allrecipes USA and Canada)