In a medium bowl, combine graham cracker crumbs, granulated sugar, and melted unsalted butter until well blended. Press this mixture firmly into the bottom of a 9-inch springform pan, then refrigerate the crust for about 30 minutes.

In a large mixing bowl, beat the softened cream cheese and powdered sugar together using an electric mixer until creamy and smooth, about 2-3 minutes. Gently mix in the vanilla extract and marshmallow fluff until fully integrated.

In a separate bowl, whip the heavy cream until soft peaks form, approximately 3-5 minutes. Carefully fold it into the cream cheese mixture using a spatula.

Pour the creamy filling over the chilled crust, spreading it evenly. Cover with plastic wrap and refrigerate for at least 4 hours, or overnight for the best results.

In a mixing bowl, combine the remaining marshmallow fluff with whipped cream, mixing gently until combined. Carefully spread it over the chilled cheesecake.

Optionally, add mini marshmallows or crushed graham crackers on top for garnish. Chill for an additional 1-2 hours before slicing.