Add milk and mix well. Cook till the mix thickens.
Pour it into a bowl, cover with plastic wrap so the wrap touches the top layer of the flour mix and set aside to cool completely.
Take butter in a bowl, add vanilla and mix well.
Now add the cooled flour mix spoonful at a time and keep mixing.
Add very little at a time and mix till creamy.
Add food colour if needed and mix well.
You can refrigerate the frosting till needed. Take the frosting out the fridge few hours before use.
Notes
1)Add flour mix little by little and keep mixing. 2)If you add too much at a time, then the mix may curdle. 3)Once all the flour mix is added, stop beating. If you keep beating then it may separate.