Step 1: Prepare the Crust: In a medium bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Mix until well combined and the crumbs are moistened.
Step 2: Press the mixture firmly into the bottom of a 9-inch springform pan. Place the crust in the refrigerator to chill while you prepare the filling.
Step 3: Make the Cheesecake Filling: In a large bowl, using an electric mixer, beat the softened cream cheese until smooth and creamy. Add the powdered sugar and vanilla extract, and beat until fully incorporated and lump-free.
Step 4: Gently fold in the 1 ½ cups of marshmallow fluff into the cream cheese mixture until just combined. Be careful not to overmix.
Step 5: In a separate bowl, whip 1 cup of heavy cream until stiff peaks form. Gently fold the whipped cream into the marshmallow-cream cheese mixture until no streaks remain. Do not overmix.
Step 6: Pour the cheesecake filling over the chilled crust in the springform pan. Spread evenly with a spatula. Cover the pan loosely with plastic wrap.
Step 7: Chill the cheesecake in the refrigerator for at least 4 hours, or preferably overnight, until firm and set.
Step 8: Prepare the Topping: Once the cheesecake is set, in a clean bowl, whip the remaining 1 cup of heavy cream until stiff peaks form. Gently fold in the remaining 1 cup of marshmallow fluff until combined.
Step 9: Spread the marshmallow topping over the chilled cheesecake. Garnish with mini marshmallows or crushed graham crackers, if desired.
Step 10: Carefully remove the cheesecake from the springform pan, slice with a hot, clean knife, and serve immediately. Enjoy!