In a mixing bowl, combine cocoa powder and powdered sugar.
Add softened butter and mix until crumbly.
Gradually pour in milk while mixing on low speed.
Add vanilla extract and a pinch of salt.
Increase speed to medium and blend until smooth and creamy.
If the icing is too thick, add more milk, a tablespoon at a time.
Taste and adjust sweetness by adding more powdered sugar if desired.
Let the icing sit for a few minutes to thicken.
Spread or pipe the icing onto your cooled cake or cupcakes.