I've not made cordial before; it was a last minute idea just to finish-up our Blackcurrant crop.
Of course I didn't have any small bottles, so I had to use the above.
The recipe I used came from The Guardian, who suggested one should use the nectar to mix with Champagne; well they would wouldn't they.
I believe the resulting fizzy drink is known as a 'Keir Korbyn'. Cheers!