Sift together the powdered sugar and cocoa powder to remove any lumps.
1 ½ cups powdered sugar, ⅓ cup cocoa powder
Add the milk and vanilla to the dry ingredients and mix to combine. Adjust the thickness by adding more powdered sugar to thicken or more milk to thin.
¼ cup milk, ½ tablespoon vanilla
Notes
Use dark cocoa powder instead of regular cocoa powder for a deeper chocolate flavor.
To achieve a glossy finish on your icing, add a small amount of corn syrup or glucose syrup.
Be sure to use real vanilla extract for the best flavor. Artificial vanilla flavoring does not have the same taste.
Experiment with the quantities of cocoa powder and vanilla extract to suit your taste preferences.
Use another kind of extract like almond, hazelnut, or orange instead of or in addition to vanilla.
Leftover icing can be stored in an airtight container in the refrigerator for a few days. It will thicken in the fridge so let it sit out for a few minutes and then stir well before using.