Add the powdered sugar, vegan butter, soy milk, and vanilla extract into a mixing bowl.
Using an electric mixer, start at a low speed and gradually increase the speed until perfectly smooth. Frosting should be very thick, but easily spreadable. If too thick, add a bit more milk. If too thin, add a bit more powdered sugar.

3 3/4 cup powdered sugar
3 tablespoon vegan butter
4 tablespoon almond or soy milk
2 teaspoon vanilla extract