In a medium bowl, combine 1½ cups cookie crumbs, butter and sugar. Press the crumb mixture into the bottom of an 8½ x 11-inch pan. Place the pan into the freezer while you prepare the rest of the dessert. You want the crust to firm up.
PREPARE THE FILLING:
In a large bowl, use an electric mixer to soften up the cream cheese and beat until creamy. Mix in the sugar, then the pumpkin and sour cream until well-combined. Add in the milk and the dry pudding mix, and beat for 1 minute.
Remove the pan from the freezer and spread the pumpkin mixture evenly on top. Spread the Cool Whip on next. Then sprinkle cookie crumbs on top.
Refrigerate the dessert for at least a couple of hours before cutting and serving.
Notes
*To make shortbread cookie crumbs, just place the cookies into a food processor and give it a few whirls... or put the cookies in a large zip baggie and smash to bits!