I first came across this in Mexico 14 years ago- I couldn’t believe I had never heard of it before! The sauce is an amazing combination of chocolate and chilli, and is rich and full of flavour. It should be made with ancho chillies, but I haven’t been anywhere that sells them, so I used ancho chilli powder which is in a little chilli kit that my husband gave me a couple of years ago. If you can’t get ancho chilli powder then you can substitute with chipotle which is pretty widely available.