Smash shortbread cookies in a Ziploc bag, until fine. For extra-fine crumbs, you can crush cookies in a food processor.
Add melted butter to Ziploc bag with crushed cookies and mix around until coated. Press crumbs into a 9×13 pan.
Bake at 350°F for about 10 minutes in the oven until golden. Let cool. Smooth together cream cheese, sugar, and 2 cups of your cool whip (or whipped cream). Pour an even layer over crushed cookie crust
Mix the milk and pudding mix together until thickened up. Pour over the cream cheese layer.
Spread your remaining whipped topping over the top and refrigerate. Top with crushed pecans if desired.