Simplify the following text for a Grade 10 native English-speaking person.
Original: He first conducted at the Metropolitan Opera ( Met ) in December 2004 , conducting LeoÅ JanÃ Ä ek 's `` KÃ t ' a KabanovÃ '' with Karita Mattila in the title role .
Simplified: He made his Metropolitan Opera ( Met ) debut on December 17 , 2004 conducting KÃ Å a KabanovÃ , with Karita Mattila in the title role .