Couple drops of imitation butter flavor (optional, if you use non-dairy butter-flavored palm oil, you can skip this)
With a hand mixer or stand mixer, beat the palm oil until softened.
Add in slowly the powdered sugar, cocoa powder, rice milk, and vanilla. Beat until mixed thoroughly and smooth.
If you need, you can adjust the thickness to your liking by adding a little bit of rice milk (1 teaspoon at a time) to make it less thick, or powdered sugar (1 Tablespoon at a time) to make it more thick.
*If you don't want to use palm oil, you can use completely softened dairy free butter and omit imitation butter flavor. You may need to add a bit more powdered sugar to get the stiffness/structure in the frosting that you prefer.