Refrigerate the can of coconut milk overnight - or 6 hours minimum
Carefully open the refrigerated can, being careful not to disturb the contents and carefully spoon to solidified fat from the top into a clean bowl. Try not to get any of the coconut water/liquid from the bottom of the can into the bowl.
With an electric mixer, start beating for about 1 minute. Stop the beater and add in the vanilla and powdered sugar. Continue beating, scraping the sides if necessary until stiff peaks form. Depending on your mixer and the brand of coconut milk you used, this will take another 1 -3 minutes.
Either use right away or refrigerate. I've heard this will last a couple of week in the fridge. It has been my experience though that it will last no more than 5 days before it starts breaking down and becoming more liquidy.
There are many recipes on the internet for canned coconut whipped topping. I've used several. They are all similar. This is simply my version.