I can't find much information about Sylvan Esso, other than that they're a duo made up of vocalist Amelia Meath and electronic musician Nick Sanborn. After being introduced via their other separate music projects, they've collaborated to bring us the sound you're hearing today.
"Hey Mami" is a stunning tune that starts with Meath's vocals as the prominent feature. Once you're almost convinced it's an acoustic track, the bass drops and the beats start, and from there the track rides out and suddenly you're singing along.
It's a song that (upon accidental first listen) stopped me in my tracks, and it's been on repeat this afternoon.