The Big Bang Theory wrapped up its sixth season with a breakthrough for Raj. Overcoming selective mutism was one of scores of watershed moments the CBS comedy celebrated under first-year showrunner Steve Molaro.

While the writer/executive producer has been with the series since season one, Molaro says this year the characters -- because the audience knew them so well -- were in a place where the series was ready to go deeper and "tell stories where things really happen to them and things matter more."

"I'm really proud of season six; it's been really satisfying and fun to see how we've been able to go deeper and push these characters," Molaro says. The Hollywood Reporter was on set for the season finale and polled the cast on their favorite moments from the season that helped propel the series to become TV's No. 1 scripted comedy on TV.

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STEVE MOLARO

"I can't pick one. Leonard and Penny saying, 'I love you'; Raj's speech in the comic book store about how they're all a community, if they have each other; Sheldon making Amy his emergency contact; Howard coming back from space. Every character has had these incredible moments this season. Raj standing in the hall convincing Lucy to go out with him because he swears he's messed up in the head. The end of the closet episode when they all tell Howard what might be in the letter and one of them is true."

JIM PARSONS (Sheldon)

"I did really enjoy the episode where Amy was sick. Her lassoing Sheldon into taking care of her goes to my point of Sheldon doing almost anything that is justified in the name of science or reason. In that case, she was sick enough that she needed to be bathed; she needed to have something rubbed on her bare chest; and by the end, she'd done so wrong that when Sheldon found out that she'd lied that she needed to be spanked. The young lady gets exactly what she wants by a young man who's doing it for different reasons. It's really brilliant."

MAYIM BIALIK (Amy)

"The spanking episode. That was fun largely because it was supposed to be off-camera, and at the last minute, Chuck Lorre decided to film it. That was really fun and awkward, right in front of the audience letting it come alive."

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JOHNNY GALECKI (Leonard)

"Penny telling Leonard she loves him is pretty big. We didn't play it as a watershed moment. It was played as if she's always known this. It was touching. I also love the moment when Leonard says, 'I know I propose a lot,' and then promises that he won't. It's one of my favorite Leonard lines to say. To put his own desire aside and say, 'You tell me when you're ready, despite what I want in my life right now and with you right now.' That's unconditional, selfless love."

KALEY CUOCO (Penny)

"When Penny said, 'I love you' to Leonard. It took her more than five years to say it. That's why now you know with Penny that whatever she does is real. You know when she said it she truly meant it. That's why now Leonard is OK with going away and knowing that they're going to be OK. We did that in one take. Steve came out and said, 'We're really happy with that. Do you want to do it again?' We didn't want to; it felt perfectly right. I told Johnny: 'It was so weird -- I became Penny in that moment.' There was no audience, just Leonard and Penny. It was a moment I'll definitely never forget."

KUNAL NAYYAR (Raj)

"I'll always remember this season. This is the season where these guys are getting to the point in their lives now where their priorities are not, 'Let's have video game night.' It's, 'I want love. I want a family. I want a relationship. I need a partner in my life.' That is the season for me; watching them shift from, 'Let's buy a time machine,' to, 'Am I going to get married to this girl? Am I going to ever find love? Am I ever going to find a partner?'"

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SIMON HELBERG (Howard)

"Sheldon and Amy deciding to get physical -- but in the context of Dungeons and Dragons. It's a really brilliantly constructed scene where they're rolling the dice to figure out which article of armor, or clothing, comes off. It's really an amazing moment and a microcosm of the show. It is the reality of these characters, yet it's very universal. It's real to them and what maybe is a small step to other people, is as big of a step to these characters as you can find."

MELISSA RAUCH (Bernadette)

"The letter episode was so special. I really loved how they showed that aspect of Howard and Bernadette's marriage. It showed the emotional component of marriage and how Howard was going through this really traumatic event, and they did it together. They've always done a good job of showing the love between Howard and Bernadette -- even though they bicker and they don't always see eye to eye at exactly the same time. I just loved how that was a dual effort of helping them come to Howard's resolution and him talking it out with her."

Which were your favorite moments? Hit the comments below with your thoughts.

Email: Lesley.Goldberg@thr.com; Twitter: @Snoodit