Crush a package of Oreo Cookies. You can set aside a few whole cookies for garnishing. Put 1/2 cup of crumbs aside and spread remaining crumbs evenly in bottom of a 9x13" pan.
Cut a square box of ice cream in 3rds evenly. I take the box apart and stand ice cream block on it's side. The three parts should fit perfectly into the pan if you put two pieces parallel and one across the bottom. Mint chocolate chip or cookies and cream flavors are a favorite, but be creative.
Microwave a jar of Hot Fudge ice cream topping until pourable. Spread evenly over top of ice cream. Immediately cover and put in freezer for a couple hours.
Remove from freezer and spread Cool Whip over top and sprinkle with remaining Oreo crumbs. Return to freezer for several hours or overnight.
Variation: Chop Reese's Peanut Buttercups, nuts, or another candy bar and press on top of the ice cream.