Preheat a baking sheet in the oven at 200C/400F/Gas 6.
For the scones, place the flour and butter into a food processor and pulse until the mixture resembles breadcrumbs. Add the sugar and pulse again, then gradually add the milk until the mixture comes together to form a dough (you may not need all the milk).
Turn the dough out onto a floured surface, knead gently and cut into four 5cm/2in rounds using a pastry cutter.
Place the scones onto the preheated baking sheet and bake in the oven for 6-8 minutes, until golden-brown. Remove from the oven and allow to cool slightly.
For the topping, place three marshmallows on top of each scone. Using a mini-blowtorch, colour the marshmallows all over. Top each scone with a dollop of whipped cream.
To serve, place the scones onto a plate and dust with cocoa powder.