Bernie Telsey and Adam Caldwell have lost track of the number of Tony Award winners and nominees they’ve cast on The Gilded Age. “We’ve joked about doing a list, but we haven’t actually done it,” Caldwell says. “And then a lot more just got added in season two,” Telsey points out. Julian Fellowes’s sumptuous HBO period drama serves as an elaborate Where’s Waldo? for the kind of people able to pick faces out of the crowd at Joe Allen, though that’s not necessarily its casting directors’ intention. In addition to their screen work, which includes Only Murders in the Building,And Just Like That …, and Sex and the City before it, Telsey and his associates have worked extensively in casting theater, from the original Rent and Wicked up through Hamilton. The series films in and around New York, which makes these sorts of actors more accessible, and according to the pair, those with stage training usually excel with period dialogue, so performers with Tonys (and also probably a few Drama Desks) tend to fall to the front of the pack. “It’s a coincidence of skill, of who’s able to elevate the language, and who has the star quality to pop in their own unique way,” Caldwell says.

Consider how The Gilded Age cast two of its leads, Christine Baranski and Cynthia Nixon (both two-time Tony winners), who play old-money sisters Agnes van Rhijn and Ada Brook. “Our job as casting directors is to come in with a list, the longer the better, and Julian within seconds was like, ‘I love Christine Baranski,’” Telsey says. As it turned out, Baranski hadn’t had the experience of doing much period work onscreen — recently, she’d primarily appeared in the present-day law offices of The Good Wife and Fight, and occasionally singing on an island in Greece — and was excited about the idea of joining the series. In Nixon’s case, Telsey and Caldwell were intrigued by the prospect of casting her against type as the shyer Ada. “You don’t think of Cynthia Nixon as being the mousy sister,” Caldwell says, “It was really exciting to see her elevate it.” The two were, individually, on the casting directors’ lists from the beginning, but once they both joined the series, it meant The Gilded Age had produced a very specific theatrical reunion: Nixon and Baranski played mother and daughter in The Real Thing in 1984. “I was a casting assistant on that!” Telsey adds, “And on Hurlyburly, when Cynthia was running back-and-forth doing both shows.”

To fill out The Gilded Age’s immense supporting cast, the casting directors brought in a wide pool and had each read for a variety of parts. “It allowed us to try different people for roles upstairs and downstairs,” Telsey says. “Usually you’re hiring for one role and reading six people. We were hiring for 12 roles and they were all in the lobby together.” Telsey and Caldwell assembled the ensemble like a very complex jigsaw puzzle: For the various society women, including Kelli O’Hara’s conservative Aurora Fane and Donna Murphy’s domineering Mrs. Astor, they had to consider how all the actors might play in a scene across from each other. “It was so fun to talk it through with Julian and go, ‘If this is where we are in interested in Donna, how does that play out for your storylines?’” Caldwell says. “There are so many women on the show, and we really wanted to define them.” Some actors came in for one type of role and ended up elsewhere. “It was rewarding to go, ‘We’d like you to meet Celia Keenan-Bolger, whether or not she’s right for this part,” Caldwell says, “and then have Julian go, ‘But wait, I’m thinking about the head housekeeper, so I’m going to write that for her now.’ That part wasn’t in the original scripts.”

Other decisions came down to chemistry between pairs. Denée Benton (who’d starred onstage in Natasha, Pierre & the Great Comet of 1812 and Hamilton) was the first name Caldwell considered for the role of Peggy, but her chemistry reads with Lousia Jacobson, whom Telsey and Caldwell knew from her work for them as reader at the Williamstown Theater Festival, sealed the deal. (Surprisingly, Carrie Coon and Morgan Spector, who play sexy industrialists, didn’t do chemistry tests — “That’s just them being fantastic actors,” says Caldwell.) Peggy’s mother is played by six-time Tony winner Audra McDonald, who is, according to Telsey and Caldwell, at the top of every casting wish list. Initially, they had to schedule around McDonald’s work in The Good Fight and the character hadn’t yet been fully expanded into the version eventually shot, but McDonald was interested in Dorothy’s trajectory. “She loved the idea, and loved where the story was going,” Caldwell says.

Even if a part initially seems small, it may pay off further down the line. Telsey points out that Michael Cerveris’s part, the valet Mr. Watson, would initially appear to be a one-day guest-player role, until the first season’s finale reveals he’s hiding a secret. “That gave us permission to get a leading player for that,” Telsey says. As the show advances into the second season, you’ll meet many more familiar theater people. There’s Laura Benanti — you might ask, “How was she not on the Gilded Age already?” to which, “Exactly,” says Telsey. Robert Sean Leonard plays a love interest for Ada; he had a friendship with Nixon after the two did a play together. Theater slash TV stalwarts Amber Gray and Jeremy Shamos also make appearances. You’ll see expanded roles for some season one ensemble players as well, a decision that came out of Fellowes writing more for these actors to do.

The fact that The Gilded Age shifts plot among its ensemble relieves some of the pressure scheduling wise. “It was like casting a repertory company,” Telsey says. Actors might be scheduled for fewer shoot days and have time to do other projects in New York, like plays or musicals, and then later on, they’ll get more involved storylines, or vice versa. It’s also a game for the audience, as Telsey and Caldwell point out: If you recognize a familiar, renowned face at those Gilded Age parties, odds are they might get more to do soon. “It’s become a running joke with every play that Adam and I work on,” Telsey says, “Actors’ agents will call and say, ‘They want an out in case they get The Gilded Age.’ I’m like, ‘But they’re not in The Gilded Age,’ and they’ll go, ‘But you’re going to bring them in, right?’ I’ve never worked on a show where we get so many calls from people wanting to be on it.”

The Gilded Age Summons Broadway to Fifth Avenue