Makes approx 16. Preheat an oven to 180 degrees/gas 4. Line two baking sheets with parchment paper. Melt the 250g dark chocolate in a bowl sitting over a pan of simmering water. Beat the butter and granulated sugar until light and fluffy and then add the demerara sugar, eggs and vanilla extract and continue to beat. Pour in the melted chocolate and whisk until smooth. Fold in the flour, baking powder and salt. You want the mixture to be lukewarm at this stage so that when you fold in the chopped chocolate, it won’t melt. Spoon dessertspoon-sized blobs on the trays, leaving a bit of a gap in between. Bake for 10-12 minutes. They will be quite soft but will harden slightly as they cool and will remain a little gooey in the centre.