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. Beat mixture until fully incorporated and smooth throughout.
03 - Gradually add heat-treated flour and salt on low speed, mixing only until just combined to avoid overworking.
04 - Gently fold mini chocolate chips into frosting using rubber spatula until evenly distributed.
05 - Use immediately to frost cooled baked goods, or refrigerate in airtight container up to 3 days. Bring chilled frosting to room temperature and stir before applying.