Mix crumbs from mix, sugar and butter thoroughly with fork in medium bowl until crumbs are well moistened. Press onto bottoms of 12 paper-lined or foil-lined muffin cups.
Beat milk and filling mix with electric mixer on low speed until blended. Beat on medium speed 3 min. (Filling will be thick). Spoon over crumb mixture in muffin cups. Drizzle with melted chocolate, if desired.
Refrigerate at least 1 hour or until ready to serve.