I have a silly question. What is the difference between IMBC and SMBC?
Similar ingredients - different technique.
For SMBC you combine egg whites and sugar and warm them to a specified temperature while stirring. Then beat the white/sugar mixture till it's like a meringue then add butter and whip till full and smooth.
For IMBC you make a hot sugar syrup and pour that into the egg whites while beating them. Once combined you add the butter and whip till full and smooth.
Lots and lots and lots of threads on these two frostings. Go to the forums tab, then select "search" from the purple line. Type IMBC SMBC (one or both). To limit the number of responses, select the "search topic title only" line.
Someone asked his very same question with the very same topic title about a week ago. If you do search here on CC, you'll find lots of great answers.