How to do fancy icing on cupcakes?that is done with a very large star tube on the pastry bagIt is about 2.5 cm across the endput the end of the tube really close to the cake, puff out icing to the edges of the cake, and lift while still squeezing and turn at the same timeWilton and several other companies make theseFind them at the better housewares departments or at Kitchen ShoppesYou could cut a cardboard covered with
aluminum foil into cone shape and tape or glue it and stickc in your pastry bag to get the same effectI have also done it with a folded, rolled
aluminum foil sheet and cut the end to suit whatever I was decorating.Other related question