Cook the coconut milk, whole milk and flour in a saucepan until it is as thick as brownie batter, stirring with a whisk frequently. It will take a good whack on the side of you pot with the whisk to get it all out when it's thick enough.
Cool until room temperature or cooler.
Stir in the vanilla.
In a stand mixer, or bowl with beaters, beat butter and sugar until the sugar is well mixed, but it will still be kinda grainy. This will take a couple of minutes.
Add cooled milk mixture and beat the living daylights out of it. It will be the consistensy of whipped cream. If it looks seperated...keep going! This will be quite a few minutes of high speed beating.
Scoop into a piping bag with large tip, or don't put a tip on and keep it as a big opening. Pipe onto cupcakes!