01 - Beat softened butter and brown sugar with electric mixer on medium speed until light and fluffy, approximately 2 minutes.
02 - Pour in milk and vanilla extract, beating until fully incorporated and mixture appears smooth.
03 - Gradually add heat-treated flour and salt on low mixer speed, mixing until just combined.
04 - Gently fold mini chocolate chips into frosting using rubber spatula until evenly distributed.
05 - Frost cooled cupcakes, cakes, or brownies immediately. Refrigerate up to 3 days; bring to room temperature and stir before using if chilled.