I started with a vanilla and chocolate ice cream, but it's up to you to use whatever flavors you like! Begin by letting the ice cream soften just a tad so it is workable but not soupy and melted (it's an art to achieve the best consistency).
Butter the bottom and sides of your pan, then spread a thin layer of vanilla ice cream on the bottom and sides, all the way to the top. Refreeze for a few minutes to harden this layer before moving onto the next.
Spread a layer of chocolate ice cream to fill the pan half way up, then refreeze.
Fill a plastic bag with Oreo cookies (or store brand), and use a rolling pin to crush them into fine crumbs. You may also try putting them in a food grater or blender. The smaller the crumbs the better! Mix the crumbs with chocolate syrup and spread over chocolate ice cream.
Spread a layer of vanilla ice cream over the crumbs, then cover and freeze.
Let set out for a few minutes then scrape the sides with a rippled or ridged spatula to create a lined look. Put back in the freezer to refreeze.
Mix equal parts whipped topping and ice cream and spread over top. Cover and put back in freezer. Let thaw for approximately 10 minutes before attempting to cut.