Using a handheld mixer or a stand mixer with the paddle attachment fitted, beat dairy-free butter and vanilla for 1-2 minutes until creamy.
Add in 3 cups of icing sugar and beat on medium until combined. As mixture thickens, add in the dairy free milk a little at a time until the mixture is smooth and creamy but still thick enough to stand up on its own. If it’s a bit thin, add the additional cup of icing sugar until the desired consistency is reached.
Finally, add in the ground cinnamon and salt to taste and mix through.