Tips: To get the ice cream layer nice and even, run an offset spatula under cold water and quickly spread over the ice cream to smooth out and make level.
For the chocolate fudge layer, work quickly and use a small offset spatula or knife. You want to be careful not to work the ice cream too hard or else it begins to melt and mix with the topping.
I like to scrape big dollops of fudge along the inner side part of the pan first. I pick up a big dollop with the small offset and scrape it against the inner top edge of the pan. I use up all the chocolate, going around the circumference of the pan to make them almost look like the outer petals of a flower or rays of sun. Then gently spread the chocolate down and inward towards the center, being careful not to press down too hard.
For the whipped cream, use a stainless steel or glass bowl and freeze for 15 minutes before whipping the cream. You could also try placing the cream in the bowl and refrigerating for 30 minutes before whipping. The colder the cream, the better the whip. —Danielle Rehfeld Colen
Melt the butter in a small pot. Meanwhile, place 9 ounces of the chocolate cookies in the food processor. Pulse a few times, then process until fine. Transfer to a 10-inch springform pan. Process the remaining 4 1/2 ounces cookies and set aside.
Pour the butter over the crumbs in the pan, stir until moist and press into the bottom of the pan using your fingers or a glass.
Bake 10 minutes and cool completely. The crumbs will harden slightly into a nice chocolate base. Place in the freezer and pull out the ice cream to soften slightly on the kitchen counter.
Spread the softened ice cream over the crumb base. A rubber spatula works nicely. Freeze until firm.
When the ice cream has hardened, work quickly to spread the chocolate fudge topping over the ice cream (see Author Notes for tips). Sprinkle with remaining crumbs, leaving a small border so the chocolate fudge peeks out and place in the freezer for at least 2 hours or overnight before serving.
When ready to serve, make the whipped cream: Place the cold heavy cream and sugar in the bowl of a standing mixer. Whip on medium-high speed until medium peaks form.
Serve each slice with a big dollop of whipped cream.