In a large bowl, cream butter, cream cheese and sugars until light and fluffy, 5-7 minutes. Beat in eggs, milk and vanilla. In another bowl, whisk flour, baking soda and salt; gradually beat into butter mixture.
Divide dough in half; shape each into a disk. Wrap in waxed paper and refrigerate 30 minutes or until firm enough to roll.
Preheat oven to 400°. On a lightly floured surface, roll each portion of dough to 1/4-in. thickness. Cut with a floured 3-in. round cookie cutter. Place a mint patty in center of each circle; fold dough over patty. Pinch to seal seams. Place on greased baking sheets, seam side down.
Bake 8-10 minutes or until cookies are golden brown. Remove from pans to wire racks to cool completely.
In a microwave, melt chocolate chips and shortening; stir until smooth. Drizzle over cookies. Refrigerate until set. Store in an airtight container in the refrigerator.
Freeze option: Transfer unrolled disks to a freezer container; freeze. To use, thaw dough in refrigerator until soft enough to roll. Prepare, bake and decorate as directed.