Preheat the oven to 190°C/fan 170°C/gas mark 5. Line a 12-hole fairy cake tin with fairy cake paper cases.
In a mixing bowl, make up the sponge mix with the egg and 75ml cold water. Beat with a handheld electric whisk for 3 minutes. Lightly stir through all but 12 of the raspberries and all of the nectarine slices, then spoon the mixture evenly between the paper cases.
Bake in the oven for 20 minutes, until golden and just firm to the touch. While the cakes are still warm, brush the tops with honey and top each with a raspberry. Dust with icing sugar and serve either warm or cold.