Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the crushed cereal, melted butter, brown sugar, and salt. Mix until well combined and the cereal is evenly coated. Press the mixture firmly into the bottom of a 9-inch springform pan to form an even crust. Bake in the preheated oven for 10 minutes, then remove and let it cool completely.
In another large bowl, whisk together the pumpkin puree, heavy cream, whole milk, granulated sugar, vanilla extract, cinnamon, nutmeg, ginger, and salt until smooth. Pour the pumpkin mixture into your ice cream maker and churn according to the manufacturer's instructions until it reaches a soft-serve consistency. If you do not have an ice cream maker, you can pour the mixture into a shallow dish and freeze it for about 1 hour, then stir it and refreeze, repeating this process every 30 minutes until the mixture is solid but scoopable.
Once the ice cream has reached the desired consistency, spread the pumpkin ice cream over the cooled cereal crust in the springform pan, smoothing the top with a spatula. Cover with plastic wrap and freeze for at least 4 hours or until solid.
In a medium bowl, beat the heavy whipping cream with an electric mixer until it begins to thicken. Add the powdered sugar and vanilla extract and continue to whip until soft peaks form.
Remove the cake from the freezer and carefully unclip the springform pan. Spread the whipped topping over the top of the pumpkin ice cream layer. Optionally, sprinkle some crushed cereal on top for added texture and flavor. Slice and serve immediately!
Notes
Use your favorite cereal for the crust. Optional garnish with crushed cereal.