In a small bowl, beat butter until smooth. Add vanilla and salt and mix until well incorporated.

Slowly add the icing sugar, little by little, until fully incorporated.

Beat on high for 1 minute - the mixture will be very, very thick and probably crumbly. Reduce the mixer speed to the lowest setting and slowly add half the milk. Beat until smooth.

Add the remaining icing sugar and milk alternately and keep beating until smooth.

Check the consistency of the mixture. Add more milk or sugar to achieve the desired or required consistency.

Take a large piping bag with a flat tip, fill with icing. Make sure to avoid air bubbles as much as possible.

Use the flat side of the piping bag to pipe strips of icing over the top of the brownies at random angles, as shown.

Pipe a few dots to serve as glue for the eyes, and put 2 eyes on each brownie.