Add the puffed rice into a large bowl.
Using a Bain marie (double-boiler), or carefully in the microwave, melt the chocolate for the base.
When melted, pour into the puffed rice, and stir carefully until everything is well-mixed (it might take a little while to get everything well incorporated).
Line a fairly large pan with foil or baking paper - mine is 37cm x 27cm (14½" x 10½").
Pour the rice and chocolate mixture into the pan and smooth over until even.
Melt the topping chocolate and then spread evenly over the rice mixture.
While the chocolate is still melted, add the toppings you want, and press down gently so that they stick to the chocolate.
Refrigerate until everything has hardened (about 30 minutes).
Break into thick shards, or cut into slices. The bark will last for up to a week in the fridge (if kept in an air-tight container). Enjoy!