Line a 30cmx20cm dish (at least 5cm deep) with baking paper.
To make the rice krispie layer, melt together the marshmallows and butter. Mix in the rice krispies and press into the bottom of the prepared dish. Place in the fridge to set.
To make the peanut butter layer, melt together the peanut butter and chocolate and pour onto the rice krispie layer.
Refrigerate until set (approximately 2 hours).
To make the chocolate ganache, melt together the chocolate and cream until smooth and glossy then pour over the peanut butter layer and refrigerate again until set.
When the bars are set, remove from the fridge and slice into bars/blocks.
These bars will keep in the fridge for up to 10 days in an airtight container.