Add cupcake liners to a muffin tin and spray with cooking oil.
Melt the butter and stir it into the graham cracker crumbs until a crumbly crust forms. Press about 1-2 tablespoons of the graham cracker mixture into the bottom of each divot in the muffin tin.
In a large bowl, whisk together the cream cheese, heavy cream, vanilla extract, and salt until fluffy. Gradually add the powdered sugar, adjusting with additional tablespoons as needed, until the mixture thickens and holds its shape when the whisk is removed.
Spoon the cheesecake mixture into the cupcake tins, leaving about a 1/4 inch at the top for adding toppings. Chill for at least one hour to set.
Use a knife to loosen the edges of the cheesecakes from the tin. Carefully remove the cheesecakes from the tin (optional: remove the papers to expose the sides of the cheesecake). Add a tablespoon of marshmallow fluff to the center of each cheesecake.
Use a brûlée torch to brown the marshmallow fluff to the desired level of doneness (from golden brown to slightly burnt). Serve immediately and enjoy!