Italian meringue buttercream

Butter is added a piece at a time to the meringue once it has cooled to room temperature. The mixture often looks curdled or soupy partway through; it comes together with more beating, as long as the butter and meringue are at similar temperatures.

IMBC is very smooth and stable at room temperature, so it suits piping and frosting cakes with sharp edges. It is less sweet than American buttercream and takes flavorings such as vanilla, melted chocolate, fruit purée and coffee well.