After few experiments, i have came out with this Swiss Meringue Buttercream that can withstand in our hot and humid weather, also don't need to care much of the room temperature or need a thermometer. This recipe work for me very well, and I hope it works for you too.
The important thing that i found out is beat the buttercream till curdles, when you see the buttercream turned to curdles, then you are safe !! I like this buttercream because it is light and less sweet, and also can store in the room temperature .
Swiss Meringue Buttercream
(recipe source: recipe adapted from The Batter Baker with minor changes, method from this video, ice cubes method from Wendy, method using hand mixer and with my own experiments)
100g egg white (3 large eggs)
227g unsalted butter, soft but still cold, cut into small equal size of cubes
1. Remove butter from fridge and cut into small cubes, set aside. Lightly whisk egg whites in a mixing bowl, place over a pot of simmering water (double boiler).
2. Add in sugar in 3 batches, whisk sugar and egg whites till sugar is fully dissolved (rub some with your fingers, if it feels grainy, it hasn't dissolved yet), take about 2-3mins.
3. Remove from heat and whisk for about 5mins till peaks are stiff, thick and glossy (Hand mixer speed at 3).
4. At this point, the mixing bowl should be cool to the touch but still slight warm at the bottom.
5. Place the bowl of meringue on top of a large bowl with few ice cubes and water.
6. With the mixer at low, add in the butter cube one by one, ensuring that each addition is well incorporated before adding the next one.
7. Beat till mixture become curdles, stop the mixer, take a spatula, continue to fold and stir till the mixture become creamy and satiny. (Even the mixture not totally smooth also ok, because when you add coloring, you need to stir and this time it will turn smooth).
8. Add colouring if desired and mix till evenly distributed.