First you'll need to line the base and spray the sides of a 20cm springform cake tin and set aside.
Blitz the oreo biscuits with a food processor until they resemble a fine crumb. Melt the butter and add this to the food processor and biscuit crumbs. Give one final blitz to incorporate.
Pour crumb into prepared tin and firmy and evenly press around the bottom and sides of prepared baking tin. I suggest using a straight edged tumbler to press crumb firmly around the sides to get a nice even crust. Once satisfied, place in the fridge to set while you make the caramel filling.
Add the cream cheese to a large bowl and beat until smooth. Note: if you remove the cream cheese from the fridge slightly ahead of time, it can beat better when it's slightly more room temperature.
Add the caramel or dulce de leche to the cream cheese and beat through until smooth and incorporated.
Finally pour in the cream and beat through for about 10 minutes. This will help aerate and lighten your cheesecake filling.
Pour filling into prepared base and allow to set overnight or for at least 4 hours.
Once the cheesecake is set, it's time to make the marshmallow by adding the boiling water and gelatine to a large bowl, stirring to dissolve. Add sugar, raspberry essence and a few drops of colouring, then beat with a hand-held beater on high for 10 minutes until thick, fluffy and sugar has dissolved.
Cover the top of your cheesecake with fluffy marshmallow and place back in the fridge to set for about 30 minutes before slicing and serving. If you'd like to pipe your marshmallow, gently spread a thin layer of the marshmallow over top of the cheesecake to help the blobs stick, then using a wide round nozzle and piping bag, blob or decorate as desired. Optional: Add and decorate top of marshmallow with freeze dried or fresh raspberries. Enjoy.