Combine ice cream, crème de menthe and vodka in a blender and blend just to mix. Add the mint chocolate chips and Thin Mint Cookies and blend thoroughly until smooth.
Add milk to thin if necessary; just enough so that it can be served with a straw.
Serve in the chilled glasses and garnish with whipped cream and additional crushed cookies.
Notes
I found it worked best to chop the cookies with a chef's knife instead of crushing them; it leaves bigger pieces and not just crumbs.