Preheat the oven to 180°C (Gas Mark 6).
Heat the sugar and the water to form a syrup. Peel the orange, remove the zest and place in a pan of cold water. Bring to the boil and blanche. Repeat this process a second time. Preserve the orange in the syrup over a low heat for about an hour.
Chop the pistachios and whisk with the ground almonds, flour, icing sugar and egg whites.
Heat the butter over a low heat until it turns into a light caramel colour, then cool and add to the mixture. Set aside to cool in the fridge.
Coat the cake moulds with butter and sugar, pour in the mixture and top each cake with an slice of orange peel. Bake in the oven at 180°C for 15 to 20 minutes.
When baked, carefully turn out the small cakes from their moulds while still hot. Pour over the syrup.
«Always keep an eye on the syrup to make sure the sugar doesn't burn. Keep on a low heat.»