This celebratory ice cream cake packs all the deliciousness of a classic sundae into one impressive dessert. A homemade hot fudge sauce does double duty here: one part is mixed with the cookie crunchies for a fudgy-yet-crispy layer in the center, while the rest gets drizzled on top for a festive look reminiscent of a hot fudge sundae. Feel free to dress up the top with sprinkles, whipped cream, cherries or keep it simple. If you’re planning to serve this as a birthday cake, I recommend making it the day before. Although not overly complicated, the recipe includes several hours of hands-off time for freezing, so plan accordingly.
a 9-inch springform pan and a pastry bag fitted with a star tip
Line the inside of a 9-inch springform pan with two overlapping pieces of plastic wrap.
Beat the vanilla ice cream in a stand mixer fitted with the paddle attachment, starting on low speed and increasing to medium, until smooth but still frozen, about 1 minute. Alternatively, use a large bowl and rubber spatula. Transfer the ice cream to the prepared springform pan and spread in an even layer with a spoon. Freeze for 2 hours.
Meanwhile, place the chocolate chips in a large heatproof bowl.
Put the 3/4 cup heavy cream, cocoa powder, 2 teaspoons vanilla extract and salt in a medium saucepan. Spray a liquid measuring cup with nonstick cooking spray, measure out the corn syrup and add to the saucepan. Cook over medium heat, whisking frequently, until just starting to simmer, 3 to 4 minutes. Remove from the heat and immediately pour over the chocolate chips. Whisk until smooth and set aside.
To crush the wafer cookies, pulse in a food processor until the crumbs resemble coarse sand, 15 to 20 seconds. Transfer the cookie crumbs to a large bowl and add 1/4 cup of the hot fudge sauce; refrigerate the remaining hot fudge sauce until ready to use. Mix with a rubber spatula until small clumps form. Set aside.
Spread the cookie crunchies over the vanilla ice cream layer and press into an even layer. Freeze for 15 minutes to set.
Meanwhile, beat the chocolate ice cream in the stand mixer fitted with the paddle attachment, starting on low speed and increasing to medium, until smooth but still frozen, about 1 minute. Alternatively, use a large bowl and rubber spatula. Spread the ice cream in an even layer over the cookie crunchies with a spoon. Freeze for 4 hours.
About 20 minutes before the last ice cream layer is set, make the whipped cream. Whisk the remaining 2 cups heavy cream, confectioners’ sugar and remaining 2 teaspoons vanilla extract in the stand mixer fitted with the whisk attachment, starting on low speed and increasing to high until soft peaks form, 1 to 2 minutes. Alternatively, use a large bowl and handheld electric mixer.
To remove the ice cream cake from the springform pan, remove the sides of the pan then flip the cake out onto a serving plate and peel off the plastic wrap. Spread a thin even layer of the whipped cream all over the outside of the cake with an offset spatula (this is the crumb coat). Freeze for 10 minutes, then add another layer of whipped cream, leaving about 1 cup of whipped cream for topping (refrigerate until ready to use). Freeze the ice cream cake for 30 minutes.
Heat the remaining hot fudge in the microwave on high power until just pourable, about 10 seconds. Pour over the top of the frozen cake and let the sauce slightly drip down the sides. Garnish the top with rainbow sprinkles. Rewhip the reserved whipped cream if necessary, transfer to a pastry bag fitted with a star tip or a resealable plastic bag with one corner cut off. Pipe the whipped cream in a decorative border around the top. Garnish with maraschino cherries and serve immediately. Store leftover cake in the freezer for up to 1 week.
Feel free to use any flavor of ice cream in place of chocolate or vanilla. To save time, whipped topping, such as Cool Whip, can be used in place of the homemade whipped cream. One 8-ounce tub is just enough to frost the cake.