In 2004, Kurstin was introduced to singer Inara George by a mutual friend, Mike Andrews. Then producing George's solo debut, Andrews hired Kurstin as a pianist for the album. Kurstin and George clicked musically in the studio and together they formed The Bird and the Bee (stylized as "the bird and the bee"). Shortly thereafter, they were signed by Blue Note Records chairman Bruce Lundvall. Described by Entertainment Weekly as "space-age pop that cunningly combines bossa nova languidity with Beach Boys-style lushness", they have since released four albums and an EP. Kurstin was nominated for a Grammy Award for Best Engineered Album for the Bird and the Bee's 2015 release, Recreational Love.  After working on tracks with artists including Peaches, All Saints, Pink, the Flaming Lips, and Kylie Minogue, Kurstin was introduced to Lily Allen. Along with other musicians, co-writers, producers and engineers, he worked on her 2006 debut, Alright, Still, which went on to achieve platinum status. For her second album It's Not Me, It's You, Allen worked exclusively with Kurstin; he co-wrote every song and played all of the instruments on the record, which he also engineered and produced. The album's first single, "The Fear", spent four weeks at number 1 in the UK, and the album hit number 5 in the US and charted in the top 10 in eight other countries. With Allen, Kurstin won three Ivor Novello Awards for his work on the double-platinum It's Not Me, It's You. Based in part on the album's success, as well as his work on a bird and the bee record, Kurstin was nominated for his first Producer of the Year Grammy in 2010.  Kurstin's first commercially available collaboration with Sia was "Death by Chocolate", released on her 2008 album Some People Have Real Problems. In 2010, he produced Sia's fifth album, We Are Born. It reached number 2 in Australia and number 37 in the US. It won ARIA Music Awards for Best Pop Album and Best Independent Release.

Answer this question "Who or what is Sia?" by extracting the answer from the text above.
Kurstin's first commercially available collaboration with Sia was "Death by Chocolate", released on her 2008 album Some People Have Real Problems.