Put the egg whites in a bowl, and whisk until firm peaks form.
In a small container, add the sugar and water and microwave (600 W) for 70 seconds.
Wearing gloves/oven mitts, take container out of the microwave. Pour this gradually into the egg whites and combine well.
If you want double the amount of buttercream, use 60 g of sugar and 20 g of water, and microwave (600 W) for 2 minutes.
Beat until the meringue becomes glossy. Bring the meringue to room temperature as you beat.
Add the softened butter to the meringue in a few batches, mixing with each addition. If you're making plain buttercream, then add a small amount of vanilla essence at this stage.
Strawberry cream: After Step 5, add 1/2 teaspoon of freeze dried strawberry powder and mix.
Cocoa cream: After Step 5, add 1 teaspoon of cocoa powder. It would also be nice if you add in a drop of rum or brandy.
Matcha cream: After Step 5, add 1/2 teaspoon of matcha mixed with a small amount of warm water and mix together.
Coffee cream: After Step 5, add 4 g of instant coffee mixed with warm water. Sprinkle in a little Kaluah for aroma.
Story Behind this Recipe
Whenever I make buttercream, I tend to have leftovers. This recipe yields an amount that should be easy to both make and use up.
After microwaving, the syrup container will be very hot, so be careful not to touch it with bare hands. Bring the butter to room temperature to avoid it separating later. When you add the butter, make sure that the meringue is at room temperature.