Complex sentence: Müller has participated in both the 2008 and the 2009 World Mixed Doubles Curling Championships, and with his partner Irene Schori, he has won a gold medal at both of these championships.
Split into simpler sentences: Müller has participated in both the 2008 and the 2009 World Mixed Doubles Curling Championships, and with his partner Irene Schori. He won a gold medal at both of these championships.