Easy cupcake frosting (butter, milk, flour, vanilla, sugar)

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Easy Cupcake Frosting and Filling
3 tablespoon Flour
1/2 cup whole milk (I use half whole milk & half coconut milk)
1/2 cup real butter (I use unsalted, but salted was recommended for better taste)
1/2 cup granulated sugar (I use organic cane sugar)
1 teaspoon vanilla extract, or other flavor if you wish.
Whisk together the flour and the milk. Heat in a small sauce pan on medium heat.Whisk continuously until it starts to thicken. Let it cook, while stirring, until you can start to see the bottom of the pan. Smash any flour lumps with a rubber spatula to keep mixture smooth.
Keep cooking mixture until it resembles thick pudding, almost a paste-like consistency.

Put this mixture in the fridge and let it cool
completely, it’s fine if it stays in there long enough to get chilly, you just don’t want it warm at all. As it’s cooling, feel free to stir it occasionally to speed up the process and keep it from forming a crust on top.  When it is chilled, you can move on to the following step.
NOTE:  I don't have a stand mixer so I used the hand held one !  it's a bit tiring and time consuming but the result is excellent !  sooooo fluffy, light and amazingly good !!!
It an electric stand mixer, beat the butter and the sugar for a minute or two until well combined and fluffy. You’ll want to use the whisk attachment on a stand mixer, not the flat paddle. Then while beating, add in the thickened milk mixture and the vanilla. Beat to combine and then scrape down the sides. Don’t be scared. It’s going to look like a goopy mess and kind of lumpy and separated like this:
But you just wait. It’s gonna blow your mind in a few minutes. Beat on med-high until it comes together and becomes light and fluffy.  It can take anywhere from 5-10 minutes.
It will transform from that sloppy mess into something gorgeous, fluffy, and incredibly light and silky.  If the time has passed and it still looks like a hot mess, just keep on beating and it should eventually come together.  Feel the mixture between two fingers to see if the sugar granules have dissolved; if not, just beat a little longer.
Use it to fill or frost cupcakes, cakes or other pastries. You can’t go wrong putting this on just about anything :)
Frosts 12 cupcakes, lightly.  I almost always double it.