Why not : This ONE is the only original recipe ? (please with your comments, I'm French, not native English speaker ; however you can answer me in english)
It seems fine to me, so you could try to report it but maybe it is not accepted because "This one" is closer to "Questa qui" even though "Questa qui" literally means "This one here".
This translation should definitely be accepted.
Why not: "This is the unique original recipe."
That was my first thought, too, but I think it's because "unique" would be an adjective here. If unica were an adjective in this sentence, it would usually go after the noun, like originale does (Questa è la ricetta originale unica.)
Wouldn't "Questa e il solo ricetta originale" mean the same thing?
Sdnza crema, solo uovi, guanciale, pepe e peccorino
It would be so nice if the lessons had a less kitchen/household -oriented touch .
This could be "Questo è l'unico manoscritto originale'.
Or am I the only one in this?