Keep the leftovers in an airtight container in the fridge for up to 1 week. It will firm up when it's cold, so let it soften at room temperature before frosting cupcakes or cakes with it.
Notes
This recipe makes enough frosting for about 12 cupcakes or to frost an 8 or 9-inch two-layer cake (20-23 cm).
You need to use softened vegan butter, but not melted. This is really important or the vegan frosting won’t get the proper consistency.
Make sure the sugar you’re using is vegan. I prefer to buy vegan granulated sugar and make my own powdered sugar.
If your vegan frosting is too thick or crumbly, add a little bit of unsweetened plant milk (soy milk is my favorite one). You want your frosting to be very thick so it will hold its shape once on the cupcakes. If your frosting is too thin, just add more powdered sugar until thickens.