Alyson Lee Hannigan born March 24 1974 is an American actress and television presenter She is best known for her roles as Willow Rosenberg in the television series Buffy the Vampire Slayer 19972003 as Lily Aldrin in the sitcom How I Met Your Mother 20052014 for which she won a Peoples Choice Award in 2009 and as Michelle Flaherty in the American Pie film series 19992012 Since 2016 Hannigan has hosted the television show Penn Teller Fool Us She also provides the voice of Claire Clancy in the Disney Junior animated series Fancy Nancy 2018present