We made it in the simplest way possible: we bashed up Oreos, mixed it with melted butter, and pressed that into the bottom of a spring-form pan.
Next, we pressed a layer of softened vanilla ice cream, sprinkled more bashed up Oreos over, and finally pressed one more layer of vanilla ice cream over the top.
I froze it for several hours before serving, then released it from the pan by blasting the sides for a few seconds with a blow-dryer.
In the past, I've put a layer of whipped cream over the top of my ice-cream cakes as frosting, but this time I decided that simple was best, so we served it just as it was, with no adornment besides the candle.
It wasn't the most attractive cake ever, but Elijah loved it, and it was enjoyed by everyone else as well. The simplest birthday cake ever!