In a microwave safe bowl, add the chocolate chips, evaporated milk, butter and vanilla. Microwave on full power for 30-40 seconds. Remove and whisk until the mixture is smooth (return to microwave for a few seconds if necessary).

Add powdered sugar and continue whisking until smooth. Use immediately. If you don't get it on what you want it on soon enough and the frosting thickens, just microwave for a few seconds and whisk again and use. Makes enough frosting for a 9 x 13 inch sized cake.