Ashanti is definitely in the running for best gift-giver -- 'cause she gave her boo, Nelly, the custom Impala of his dreams for his 49th birthday.
Celebrity car broker Ronnie Garber tells TMZ ... he got a call last week from DJ Envy, saying Ashanti was looking for a specific ride to give Nelly for his big day -- and needed it in Atlanta by Halloween night, a couple days before his birthday.
We're told the artist wanted a custom 1962 Impala convertible -- the candy apple blue ride is equipped with a Corvette L's motor and a sound system with Nelly's logo on it.
She gave him the ride at his big army-themed bash, too ... when he was presented with his cake onstage, she told him about the gift she got him, which set off some fireworks ahead of the reveal.
We're told Nelly wasn't just happy, but he got emotional -- saying it was his dream car from when he was a kid, so it rightfully is goin' down for him as the best gift of all time.
As for the custom car, we're told it set Ashanti back well over $100k ... but it sounds like it was worth it!
As we reported, the 2 restarted their relationship earlier this year, being spotted out together quite a bit even jamming out together to Usher's "Nice & Slow" -- a potential nod at their romance's pace.