For the list of levels with this blocker, see here.
Two-layered frostings are single-tile stationary blockers that takes two tries to destroy. When degraded once, it becomes a one-layered frosting. These blockers can be destroyed by an adjacent match, an effect of a special candy (including jelly fish), or a cake bomb explosion. Jelly can hide under this type of blocker.
Here is the difficulty of destroying a Two-layered Frosting: