Preheat the oven to 180°C/160°C fan oven/Gas Mark 4. Grease three baking sheets. Cream together the butter and sugar. Gradually add the eggs and vanilla extract.

Sift in the flour, add the orange rind, then sprinkle in the white and dark chocolate. Mix the dough together with your hands.

Knead lightly, then wrap in clingfilm. Chill the cookie mixture for at least 30 minutes.

Divide the mixture into 26 pieces and roll each into a ball. Flatten each one slightly to make a disc, then put them on the baking sheets, spaced well apart. Bake for around 10 to 12 minutes or until golden.

Leave on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.