If you've never added chocolate to chilli then prepare to be amazed. I was a true sceptic that a small amount of chocolate could really make that much difference to a big vat of chilli, but it really does! It adds body to the recipe and balances out the flavour to make it super rich. (You need to use strong dark chocolate for this, which is bitter more than sweet).
It also makes the colour deeper, transforming the chilli into a deeper silky shade of brown!