Beat together the butter, sugar, egg, vanilla, flour and baking powder until evenly mixed. Stir in the cranberries and chopped chocolate.
Take heaped teaspoons of the cookie mixture and space them well apart in a greased shallow roasting tin or on a baking sheet, as the cookies will spread quite a bit when cooking. (You will need to cook the mixture in 2 batches.) Place the tin or sheet on the upper rack of the halogen oven.
Set the temperature to 175°C (347°F) and bake for 10 minutes. Leave to cool slightly, then transfer to a wire rack and cook the remainder of the mixture in the same way.