Step 1: Prepare your pan. Lightly grease a 9-inch springform pan with cooking spray. You can also line the bottom with parchment paper for easier removal.
Step 2: Make the Rice Krispie crust. In a large pot or Dutch oven, melt the butter over low heat. Add 1 (10 oz) bag of mini marshmallows and stir continuously until completely melted and smooth. Remove from heat.
Step 3: Combine with cereal. Quickly add the 8 cups of Rice Krispies cereal to the melted marshmallow mixture. Stir until the cereal is evenly coated.
Step 4: Press the crust. Transfer the Rice Krispie mixture to the prepared springform pan. Using a piece of parchment paper or buttered hands, firmly and evenly press the mixture into the bottom of the pan to form the crust. Set aside to cool while you prepare the filling.
Step 5: Prepare the cheesecake filling. In a large mixing bowl, beat the softened cream cheese with an electric mixer until smooth and creamy. Add the powdered sugar and vanilla extract, continuing to beat until well combined and fluffy, scraping down the sides of the bowl as needed.
Step 6: Whip the cream. In a separate, clean, cold mixing bowl, whip the heavy whipping cream with an electric mixer on high speed until stiff peaks form.
Step 7: Combine filling. Gently fold the whipped cream into the cream cheese mixture until no streaks remain and the filling is light and airy.
Step 8: Assemble and chill. Pour the cheesecake filling over the cooled Rice Krispie crust in the springform pan. Gently spread it evenly with a spatula. Cover the pan loosely with plastic wrap and refrigerate for at least 4 hours, or preferably overnight, until the cheesecake is fully set.
Step 9: Garnish and serve. Once set, carefully remove the springform ring. Garnish with extra mini marshmallows or sprinkles if desired. Slice with a sharp, warm knife for clean cuts and serve immediately.