In a jug or bowl, whisk together the whole milk, double cream, sugar, cocoa powder, and vanilla extract until smooth and the cocoa is fully dissolved.
Pour the mixture into your Ninja Creami pint container, stopping just below the fill line.
Freeze for 24 hours on a completely flat surface.
Once fully frozen, remove the pint lid and place the container into the Ninja Creami. Process once on the Ice Cream setting.
While it spins, toast the marshmallows: place them on a small tray and broil in the oven for 1–2 minutes, just until golden (watch closely so they don’t burn). Let cool slightly.
When the first spin finishes, create a small well down the centre of the ice cream and add the toasted marshmallows, crushed graham crackers, chocolate chips, and 1–2 tablespoons of milk to help blend.
Process again on the Mix-In setting until the s’mores pieces are fully incorporated.
Serve immediately for a soft scoop or return to the freezer for a firmer texture.