Cream the butter and sugar until light and fluffy.
Add the plain flour and rice flour, mixing until a soft dough forms.
Press into a lined 13 × 9-inch tray and prick all over with a fork.
Bake at 160°C fan / 180°C conventional for 25–30 minutes, or until beautifully golden. Leave to cool completely.
Add everything to a saucepan over a low heat.
Stir continuously until everything has melted together.
Continue cooking low and slow until the caramel thickens, then gently increase the heat, stirring constantly until it reaches 118°C.
Pour over the cooled shortbread and leave to set.
Melt the milk and dark chocolate together, pour over the caramel, decorate with white chocolate curls and chill until set before slicing.
