In a large mixing bowl with an electric hand mixer or in a stand mixer, beat butter until creamy for about 1 - 2 minutes. Add in vanilla extract and beat until smooth for about 30 seconds.
Sift in the cocoa powder, 1.5 cups of powdered sugar, and 2 tablespoons of almond milk. Mix on LOW speed until creamy for 1 - 2 minutes, stopping occasionally to scrape the sides of the bowl with a rubber spatula. If the buttercream is too thick add 1 - 2 additional tablespoons of almond milk. If it is too thin, add up to a ½ cup extra powdered sugar, but start with ¼ cup.
Milk: Use almond milk, oat milk, cashew milk, or your favorite plant-based milk.Storing: For best results, store leftovers in airtight containers in the refrigerator for up to 2 days. Let it come to room temperature before frosting your cake or cupcakes.Serve with these gluten free chocolate cupcakes or these healthy vanilla cupcakes.