Season 9, Episode 1 - The Matrimonial Momentum
Aired September 21, 2015
When Penny and Leonard arrive in Vegas to get married, Penny is still thinking about Leonard's admission that he kissed another girl. Meanwhile, Sheldon doesn't know what to think after Amy calls time on their relationship.
Season 11, Episode 12 - The Matrimonial Metric
Aired January 4, 2018
When Sheldon and Amy put their friends through a series of secret experiments to determine who should be their best man and maid of honor, Penny's true feelings about Amy are revealed.