Mix graham cracker crumbs, melted unsalted butter, and granulated sugar in a medium bowl until resembling wet sand. Press firmly into the bottom of a 9-inch springform pan and set aside.

Beat softened cream cheese in a large bowl using an electric mixer on medium speed for about 2 minutes until smooth. Gradually add powdered sugar and vanilla extract until fully incorporated and fluffy.

Gently fold in mini marshmallows into the cream cheese mixture using a spatula, ensuring even distribution without overmixing.

Pour heavy whipping cream into a separate bowl and whip on high speed until stiff peaks form, about 3-5 minutes. If using gelatin, dissolve it in cold water per package instructions before mixing into the whipped cream.

Carefully fold the whipped cream into the cream cheese and marshmallow mixture until smooth and fluffy, ensuring no streaks remain.

Pour the filling into the cooled crust, smoothing the top with a spatula. Optionally create a swirl or keep it flat.

Cover the cheesecake with plastic wrap and refrigerate for at least 4 hours or ideally overnight to set.

Remove the sides of the springform pan. Slice with a knife dipped in hot water for clean edges, and serve with fresh berries or chocolate sauce.