Line the base of a 20 cm square tin with two layers of clingfilm. Melt the chocolate and coconut oil in a heatproof bowl over a pan of gently simmering water, making sure the base of the bowl doesn’t touch the water. Stir occasionally. Remove from the heat and leave to cool for 5 minutes.
Put the marshmallows, peanuts, cherries, popcorn and biscuits in a large mixing bowl. Pour in the chocolate and mix well until everything is coated. Tip into the prepared tin and press down well with the back of a spoon. Sprinkle with dried rose petals. Put into the freezer for 2 hours to set, then remove and cut into large squares to serve.