Nutella icing for cupcakes

[GarnishWithALemonTwist]

Would somebody have an easy recipe to make nutella icing for cupcakes but not with cream cheese please. Also, if I don't have any gadgets, what's the best way to apply the icing? Do the cupcakees need to be completely cold before applying the icing? How long will the icing take to get hard? Thanks so much. xx

250g icing sugar
80g unsalted butter at room temp
25 ml whole milk
80g nutella,

mix it up and bung it on, I uses a knife to smooth it over, it never really got hard, I did put it on cold cupcakes.