Just want to start by saying that it looked much nicer with the candles on it and lit. But it's difficult to take photos and video at the same time, while singing and keeping track of three other kids.
springform pan, parchment or waxed paper, ziploc bag, rolling pin, freezer (duh)
One package Oreo cookies, one half-gallon cookies 'n' cream ice cream, one container Cool Whip, one jar or bottle of fudge sauce
Have the Cool Whip mostly thawed. Cut a round of parchment paper to fit in the bottom of your springform pan. This is not necessary, but I did it in case I wanted to slide it off the base of the pan onto the plate. I didn't, I just put the base right on the plate, but it was nice to have the option.
Put half the package of cookies in a ziploc and smash them with the rolling pin. You want small pieces, chocolate chip size or smaller. Because of their cream filling, the cookie bits will clump together and stick to the bag. This is fine. Dump the bits into the pan, lay the bag flat and use a knife to scrape each side inside the bag, emptying it into the pan before flipping to do the other side. Spread the crumbs as flat as possible in the base of the pan. Really squish them down. Use the bottom of a glass, or a piece of parchment, or an offset spatula if you want. I didn't find a tool that worked really well, because it's all just plain sticky, but do your best. If you don't think they are sticking together enough you can add some melted butter like you would if you were making a graham cracker crust. I did not add any butter because the next step is to spread a goodly amount of the fudge sauce over the cookie crumbs. This is also difficult because of the stickiness. Just try to get it evenly distributed and try not to cuss. The fudge sauce will help hold the crust together when you freeze it. The idea here is layers, but mushing it up tastes fine, too. Once you have a fairly dense and even distribution of a gooey, chocolate mess in the bottom of the pan - freeze it for 15-30 minutes.
After 15 min or so, take your ice cream out of the freezer so it can soften a bit. You want it spreadable, which is actually almost melted but not quite. Soft but not drippy. Get the crust out of the freezer. Put a circle of whole cookies around the edge of the pan. The ice cream will hold them in place when you spread it in a one and a half inch (1 1/2) layer. Spread another layer of fudge over the ice cream and freeze for 30min to 1 hour, or more depending on your freezer. When you deem it firm enough, spread a layer of Cool Whip over the fudge as high as the tops of the cookies, or however much you like. The Cool Whip is the frosting, and is the easiest to spread. Cover the whole thing with plastic wrap and put it in the freezer for a few hours so it freezes solid.
When you are ready to serve, you can drizzle fudge topping on it if you have any left, and you need to spring it from the pan and let it sit out for 10 min or more so it is soft enough to cut.
I have enough ice cream and cool whip left over to make another cake, but I used a whole package of cookies and almost all the fudge. I'm estimating it cost me less than half of what I would have spent buying one ready-made, all things considered.
This cake could be made with various ingredients. Try a graham cracker crust, cheesecake ice cream, strawberry topping. Or try a chocolate chip cookie crust (mix crumbs with 1/4 cup melted butter), cookie dough ice cream, a layer of peanuts, etc. Ooh, how about vanilla ice cream, a very thinly sliced Snickers layer, and peanut butter cookies for the crust and sides. If you spread the Cool Whip layer smooth enough and freeze it long enough you can use decorating gel to write on the cake. Or just put sprinkles on it, though they will melt into little puddles of color. Mix and match! Have fun!