01 - Beat softened butter and brown sugar with hand mixer or stand 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, mixing on low speed until just combined. Do not overmix.
04 - Gently fold mini chocolate chips into frosting using a spatula until evenly distributed throughout.
05 - Use immediately to frost cooled cupcakes, cakes, or brownies. Refrigerate for up to 3 days; bring to room temperature and stir before using if chilled.