I just wrote a long review of the finale of Louis C.K.'s amazing Horace and Pete, which included a few emailed thoughts from C.K. on the series. One aspect of what he wrote was so detailed and lovely that I didn't want to edit it down for the sake of squeezing it into the review, so that's coming up just as soon as I have popsicles in the car...

I mentioned to C.K. how much I loved his performance in the moment after Amy Sedaris' Mara has walked out of the bar, and he told me that Sedaris had improvised the whole performance, changing it up in every rehearsal and every take. He then elaborated: 

I had a scene written in that spot about a woman coming to interview for the bartending job. And the scene written was just a nice conversation. And the woman was worldly and loving and open.  She was a Marine and a veteran who was traveling and wanted to come home to Brooklyn.  It was meant to be just a pedestrian pleasant moment that interrupted Horace's grief randomly and reminded him that there is more in the world.   And then she puts the song on the jukebox and leaves. The character was meant to be of no consequence but just, I don't know...  
Anyway the actress that I wrote it for couldn't do it, and Gayle Keller, my casting director, suggested Amy, who I have wanted to use for a long time in anything.
Amy came to read for it the Sunday before we shot it.  She was fun and joyful in person.  We started to read the written scene  But before we even got through it, I stopped her and said, "Just do it yourself. Just say whatever you want. Let's just try it without the written dialogue." And her very first attempt at the scene was so energizing. My jaw was in my lap.  And it took the scene to a place beyond what I had intended and beyond even my complete understanding of what was great about it. I just knew it was great and just right for that moment in the show. We rehearsed it on set twice and we did three taped takes. After each time, I would talk to her a little bit.  About  the shape of the scene. I told her what i was going for.  What I liked that she was doing.  But she never repeated anything.  Generally I hardly said anything to her.  I didn't want to tamper.  Every word of her dialogue was imagined and invented by her. I didn't know she was going to say or that she was going to wear that weird dress. Or the blank button. I didn't know she was going to hug me when she showed up or what she was going to say. All I said was, "Come in and say you're here for the bartending job and insist in whatever way you want that we need to do it now, chat for a while, then put on the song and leave."  She found that waitress wanted sign by the door from a scene I had written for Alan (Alda) but we never shot it.  It had nothing to do with this scene because we were looking for a bartender not a waitress.  But it didn't matter.  She came in with that sign every take and you can tell we used the last take because she ripped the sign in half, forcing us to make this the last one and her ripping that sign is a moment I'll never forget.  
In this way Amy was just a force.

The moment that you singled out is genuine because I was startled and surprised by her energy every time we did the scene. The feelings I was having about Pete were not acting at all.  It was very intense. Every time we did the scene — which was always a complete take from when Horace walks down the stairs until the lights go out — it was a real thing to me. It was an insane ride.  Ricky the cop, Sylvia, Amy, Paul Simon and then Pete and then the end. I still haven't recovered from three takes of that. Amy was like an angel that came from outside of the show and yet belonged so completely in it.  She was key to the scene and therefore the conclusion to the story and yet I didn't know it would be her until a week ago. 
Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com