Melt the butter in a small saucepan.
Once the butter is melted, add the cocoa powder and stir well until combined.
Turn down the heat and set it aside. The cocoa and butter mixture should be very thick—like a paste.
Allow it to cool for a few minutes and transfer it to a mixing bowl.
Add in the milk, vanilla, and powdered sugar.
Using a hand mixer, mix the ingredients until they're smooth and creamy and all the powdered sugar has been incorporated.
Add a little more powdered sugar to adjust the consistency of the frosting.
Frost your brownies, cake, or cupcakes, and enjoy!
