Hi Carbcutter

I'd never heard of cornichons either, but I've heard of gherkins! Mind you I hate pickled anything, so have never had them.

On the Sainsbury's site they say that
Pickled gherkins - midget are 5.5 g carbs per 100 g - all of which is sugar.
Pickled gherkins in sour or ordinary vinegar are 2.5 g carbs
Pickled gherkins in sweet vinegar are 5.5 g carbs

So just make sure that you do not have ones in sweet vinegar. I would imagine that 100g of gherkins is quite a lot so you could easily add them to your diet.