hi Mimi, this is an amazing buttercream and I use it almost exclusively for my buttercream fillings and cakes. I use ratio 1 part egg whites: 1.5 parts sugar; 2 parts butter (all by weight). I used to use 1-2-3 ratio but found that this 1-1.5-2 ratio seems more stable. I even has success stenciling on it, believe it or not!
There is a great instruction on Three little blackbirds blog: http://www.threelittleblackbirds.com/tag/swiss-meringue-buttercream-recipe/
Good luck!
Maria @ http://www.facebook.com/rooneygirlbakeshop or http://www.rooneygirlbakeshop.com
