Heat oven to 190C/fan 170C/gas 5. Beat the butter, sugars and egg until smooth, then mix in the flour, chocolates and cherry pieces and ½ tsp salt. Spoon onto non-stick baking sheets in large rough blobs - you’ll get 20 out of this mix. Make sure they are well spaced as the cookies grow substantially as they bake. The raw dough can be frozen.
Bake for 12-14 mins until just golden, but still quite pale and soft in the middle. If baking from frozen, give them a few mins more. Cool on the sheets for 5 mins, then lift onto racks with a fish slice and leave to cool completely.