I made these cupcakes for my brother's graduation in June this year. The cupcakes themselves are standard vanilla with vanilla buttercream frosting (coloured green as this was the colour of the trim on his graduation gown). The little caps are made from mini Reese's Peanut Butter Cups turned upside down with After Eight chocolates on top. I bought some ready made icing in a tube to stick the two together and also used it to stick the tassels to the top of the caps (tassels are made from Regal Icing rolled into strips).
The peanut butter cups are not easy to come by in Northern Ireland so I had to buy them off eBay. They were a bit expensive but I think the end result was really cute (though if I make them again I think I'd refrigerate the peanut butter cups to avoid the chocolate peeling off the sides when the wrapper is taken off, which happened on a few of them). Alternatively you could use Rolos but they are slightly smaller than the peanut butter cups.