In a sauce pan add all purpose flour and sugar. Add milk and whisk until there are no lumps.
Heat it on low flame mixing it continuously.
In about 7-8 mins, the mixture turns very thick and when you remove the whisk, the custard should not fall off of it. Remove from heat.
Cover this with cling wrap in such a way that it touches the top of the custard. This will stop the top from drying too much and it doesn’t form a thick layer.
Refrigerate this custard if not using immediately. But ensure that the mixture is cooled down completely before adding butter.
In a mixing bowl, add butter and beat it until it is fluffy.
Now add the prepared flour custard and beat it along with vanilla essence for 2-3 mins.
The frosting turns light and fluffy. Add any food color if you wish.
Transfer the mixture into a piping bag with relevant frosting nozzle and frost the cake. The frosting doesn’t melt or turn runny unlike whipped cream.