In a food processor, finely crush the biscuits. Add in melted butter and pulse until combined.
Press the biscuit mixture into the bottom of 6 large muffin trays and put in the fridge to set.
Meanwhile, combine the milk chocolate and butter and microwave in bursts of 30 seconds on medium until smooth and melted.
Divide the chocolate mixture evenly over the biscuit bases.
Gently press a large marshmallow into each S'mores cup and return to the fridge to set.
Once set, toast the marshmallows using a cook's blow torch until are brown and crunchy. If you don't have one, place the tray under the oven grill for 30 seconds to 1 minute until golden.