Combine chocolate chips, milk, butter and vanilla in microwave-proof bowl. Microwave on full power for 30-40 seconds.
Remove and whisk. If chocolate chips are frozen like mine, microwave again for 30 seconds. Whisk again until chocolate chips melt and mixture is smooth.
Add powdered sugar by sifting to ensure smoothest frosting and continue to whisk until smooth.
Spread the frosting while still warm. This will help the frosting spread easier and keep you from damaging the cake or brownies.