Preheat oven to 350°F (180°C). Line 9-inch square pan with enough parchment paper to overhang edge of pan; set aside.
Toss together pie crust mix, cookie crumbs and sugar. Cut in butter with fingertips until mixture resembles coarse crumbs. Press into bottom of prepared pan.
Bake for 25 to 30 minutes or until golden brown and set. Let cool completely.
Bloom gelatin sheets in water as directed on package. Transfer sheets to small saucepan with milk; heat for about 5 minutes or until gelatin is completely dissolved. Let cool completely.
Prepare mousse using cooled gelatin milk according to package directions; set aside.
Spread mousse mixture over prepared base. Refrigerate for 2 to 3 hours or until set.
Using parchment paper as handles, transfer to cutting board; sprinkle with crushed peppermint candies. Cut into bars or squares.