Can you put an all-butter buttercream under fondant? Thanks.
Sure you can! I make fondant cakes with SMBC all the time.
Absolutely can! We use that under fondant most of the time here in the UK. Use 1:2 ratio of butter:sugar and a hot knofe to smooth and it will be plenty firm and crusted to hold the fondant.
Just make sure you chill the meringue buttercreams until hard, otherwise it'll be really difficult to cover with fondant!