On the day of the party, I took them out of the freezer. You don’t need to let them defrost all the way before decorating. Put a bit of frosting in the center. You don’t want the next layer to squeeze it out the sides, so do not frost all the way to the edge. The top is piped with a 1M tip. Normally, I decorate a cupcake by starting on the outer edge and spiraling in toward the center. A rosette is done the opposite way. You start in the center and spiral out to the edge.
* My one warning is to make sure your cakes are level and are frosted evenly. I had some problems with tippy ones that I had to prop up until right before the party. The ones that were leveled well had no problem.