Here is my recipe for Italian Meringue Buttercream, which is a light creamy icing and filling for cakes, it is quite a bit less sweet than regular buttercream.
You will need a digital or sugar thermometer, small saucepan, stand mixer.
200gm (approx 1 cup) Castor Sugar - or regular, Castor just dissolves quicker.
2 teaspoons Lemon Juice - or a pinch of Cream of Tartar - do use one or the other as it strengthens the protein in the egg whites.
3 XL Egg Whites
Dash of Vanilla - or flavour and or colour of choice
250gm Softened Unsalted Butter
Soften the butter in a bowl until it is much lighter in colour and creamy smooth, almost white - if you use your stand mixer to do this first, then thoroughly clean the bowl with detergent and dry completely before beating the Egg whites, as the egg whites will not beat if there is ANY grease in the bowl or on the whisk.
In a saucepan over a medium heat, bring the Water, Sugar and Juice to the boil.
In a stand mixer, begin whisking the Egg whites until soft peaks form, and then just turn it off or down to very low whilst you continue boiling the syrup until it reaches 115°C - don't over beat the egg whites, you want them to be at soft peak stage or just beyond, not dry and stiff.
Once you have the syrup at the right temp, be ready for action, as you need to move quickly now, remove from heat and let it sit for a few minutes until it stops boiling, then carefully add a very thin stream of the hot syrup into the egg whites in the mixer bowl, as the whisk is still mixing at a medium speed, do it in a very steady stream towards the edge of the bowl so you don't end up with strands of toffee stuck to the side of your mixer, but add it quickly otherwise you will cook the egg whites!!
When all the Sugar syrup is incorporated, add the Vanilla and or Colour - then crank your mixer back up to full, and let it do it's thing until the sides of the bowl feel cool to touch, - This can take up to 15 - 20 minutes.
Your egg whites should have really increased in volume and be nice and shiny.
Once the bowl no longer feels warm to touch, then begin adding your softened beaten Butter into the bowl, a spoonful at a time, until it is all incorporated. The volume will decrease, this is OK, just let it go. When all the butter is in there, scrape down the sides of the bowl, and beat for a while longer, until you are happy it is a nice even mix.
Then you are ready to use it to decorate, and it can be split into smaller batches to be coloured etc.
This Buttercream is fluffy textured, lighter in taste than regular Buttercream, and no where near as sweet as regular buttercream. Wonderful to pipe as well, you can use it to create decorative borders, or write etc.