Step 6
In small microwavable bowl, microwave 3/4 cup chocolate chips uncovered on High 60 seconds; stir halfway through. Continue to microwave in 15-second increments until chips can be stirred smooth; cool 10 minutes. In large bowl, beat butter and melted chocolate with electric mixer on medium speed until blended. On low speed, beat in powdered sugar, milk and vanilla, scraping side of bowl occasionally, until smooth and creamy.