A light, smooth icing that is velvety rich and a favorite in pastry kitchens.
Combine 225g sugar and 150ml water in a medium-sized saucepan. Stir with a wooden spoon, until the mixture is the consistency of wet sand.
Use a wet pastry brush, clean all the sugar crystals from the sides of the pan to prevent the sugar from crystallizing.
Heat over medium heat, undisturbed until the syrup reaches soft ball stage, around 240°F (when you drop some syrup into a cup of room temperature water, you should be able to roll it into a ball)
Meanwhile, place egg whites in a stand mixer fitted with a whip attachment, beat to aerate. Add 65g of sugar and beat till soft peaks form.
As soon the syrup reaches the sift ball stage, slowly drizzle the hot syrup down the side of the bowl with the motor running. Take care not to pour the syrup onto the whip, or the syrup may splatter.
Once all the syrup has been added, keep mixing until the bottom of the bowl feels cool to the touch and the meringue has cooled down to body temperature.
Remove the Whip attachment and replace with the Paddle attachment. IMPORTANT!
Add butter one cube at a time, beating well after each addition until all the butter has been incorporated and is very smooth.
Use immediately or refrigerate in an airtight container in the fridge for up to two weeks or in the freezer for up to one month. To use buttercream that has either been refrigerated or frozen, first allow to come to room temperature then beat until smooth and spreadable again.