This buttercream is very good, a useful invention for the busy cooks - it tastes almost the same as the classic milk buttercream, cooked on the stovetop.
It takes about 10 minutes to cook and some time to cool down - I warmly recommend it, you can use it for any cake you like.
In a heat resistant dish which you will also put in the microwaves, beat the egg yolks and the sugar using a whisk.
Add in flour and mix well to make sure there are no lumps.
Now comes the milk, pour it little by little, mixing well each time so that the mixture is smooth.
Put it in the microwave for 4-5 minutes - and PAY ATTENTION - take it out after each minute and whisk.
Each time you take out the cream to mix, you will notice it gets thicker. If it gets thick enough sooner - say, after 3-4 minutes, don't put it back in the microwave.
In this hot mixture tip the butter and the vanilla extract, whisk well.
And it's done, you now have the perfect cream for different cakes - and it's very quick as well.
Enjoy!