my sons birthday is coming up and I really would like to do the Reeses pb cup....any suggestions on how to do the ribbed chocolate?

If I was doing it I'd ase a crusting buttercream, and press a dowel rod around the cake. Then do poured ganache or a chocolate glaze on top.

My first thought is to use the bottom of the giant cupcake pan and cover in ganache. I think proportion wise I wouldn't fill it all the way and I would make 2 but that's up to.

Here's Reese's PB cup cake that has directions for the "cup" in the comments:

http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1211796

HTH

lol jan- I was just going to post that one. I'm trying my hand at it today!

If it were me, I would make a peanut butter cake, cover it in a layer of ganache, and then cover it with modeling chocolate. I would just mold the side ridges by shaping the modeling chocolate.

Here's another one though that looks like they just did it out of chocolate buttercream and it looks great too.
http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1431583

They made one on Ace Of Cakes once. I don't remember the episode . It was not a whole cake but the PB cup sat on top. maybe someone else can remember it and you can find it on HULU or On Demand.

Actually the Ace of Cakes episode is where I got my idea for one. I don't know if they used ganache to cover it first, but I do know they covered it in Modelling chocolate, and then just molded the ridges out of it. They did not make tiny little bitty ridges, they were bigger, and I think it looked great since the cake is so big. On the cake they made they put a breakdancer on top of it spinning on there head, looked pretty cool.

I think this is the episode. It says it is, but I cannot actually view it here at work.
http://sweetcheeksbakerynyc.blogspot.com/2009/06/ace-of-cakes-breakdancer-cake-with.html

I made mine today! It was SUPER easy! http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1624340

this is my all time favorite.. I am so going to make one of these http://cakecentral.com/modules.php?name=gallery&file=displayimage&pid=1567196