Mint-Chocolate Chip Ice Cream Cake

Line two 8-inch round cake pans with plastic wrap. Divide ice cream between pans and pack evenly to make two smooth layers. Freeze until solid, at least 6 hours, then remove from pans using plastic wrap; wrap until needed.

For cake: Preheat oven to 350°. Coat three 8-inch round pans with nonstick cooking spray and line bottoms with parchment paper. Spray again; set aside. In a very large bowl, whisk together flour, sugar, baking powder, salt and baking soda.

In a medium saucepan, combine the water, butter and cocoa powder. Bring to a boil over medium-high heat, stirring frequently. Pour hot cocoa mixture over flour mixture. Beat with an electric mixer on medium-high speed until thick and smooth, about 1 minute. Beat in milk. Beat in eggs, one at a time. Beat in vanilla.

Divide batter among prepared pans. Bake until a toothpick inserted in center of cakes comes out clean, 17 to 20 minutes. Cool in pans on a wire rack. Remove from pans; discard paper.

For hot fudge: In a 1-quart heavy saucepan, combine cream, corn syrup and salt. Cook over medium heat until just simmering, stirring occasionally. Remove from heat. Add chocolate (do not stir); let stand 5 minutes. Stir until smooth. Stir in vanilla. Set aside to cool slightly. (Fudge can be prepared 10 days ahead and refrigerated. It will get very firm; just microwave about 15 seconds to soften.)

For fudge crunch: Place cookies in a large zip-top bag. Crush with a rolling pin, aiming for a mixture of pebbly bits and crumbs. Transfer to a bowl. Add 1/2 cup of the cooled hot fudge and the peppermint extract, if using. Stir until well-blended.

For whipped cream: In a small bowl, whisk together the cold water, vanilla and gelatin. Let sit 5 minutes. Microwave until gelatin granules are just dissolved, 5 to 10 seconds (do not actually heat the mixture).

Place cream and powdered sugar in a medium mixing bowl. Beat with an electric mixer on low speed to combine, drizzling in gelatin mixture as you beat. Increase speed to medium-high and beat to stiff peaks. Use immediately or refrigerate, covered, for up to 3 days.

To assemble cake: Line an 8-inch springform pan with two perpendicular sheets of plastic wrap, leaving at least 10 inches of overhang on all sides. Use a large serrated knife to slice the domed top off each cake layer, so they are level. Place one cake layer in the pan, cut side up. Spread with half the cookie crunch mixture. Unwrap one ice cream layer and place in pan. Repeat with second cake layer, remaining cookie crunch and remaining ice cream. Top with the final cake layer, cut side down (the layers will go above the edges of the springform pan). Bring excess plastic wrap up and over the cake on all sides and wrap tightly. Freeze until firm, at least 6 hours. Before serving, spoon extra hot fudge over cake, nudging it to the edge with a spoon so that it drips over the sides. Top with whipped cream and garnish with crumbled cookies.