UPDATED: The duo have signed multiple-year overall deals with ABC Studios and will board the Wonderland-set spinoff, which is scheduled to shoot a teaser in April.

ABC is bulking up its potential Once Upon a Time spinoff.

Once consulting producer Jane Espenson and Zero Hour's Zack Estrin have inked multiple-year overall deals with ABC Studios and boarded the network's now Wonderland-themed effort, The Hollywood Reporter has learned. Espenson will serve in the same capacity, while Estrin will be an executive producer.

STORY: ABC Eyeing Potential 'Once Upon a Time' Spinoff

Under the pact, they'll join Once creators/executive producers Eddy Kitsis and Adam Horowitz (who are penning the pilot) on the spinoff. The project, first announced in February, was previously set to revolve around the Mad Hatter (who has been portrayed by Sebastian Stan on the ABC drama), with producers noting at this month's PaleyFest that they had "no plans" to recast anyone considering the actor's busy schedule. The project is now set to take place in Wonderland.

The Once team will shoot a short "teaser" presentation in April and, should it move to pilot, film that in late July or August. Casting is currently under way to fill roles including Alice, The Knave and the mysterious Amahl. No casting has been announced.

STORY: 'Once Upon a Time' at PaleyFest: Storybrooke's Origins, New Lands and 9 Season 2 Teases

Espenson, whose credits include Buffy the Vampire Slayer, Dollhouse, Warehouse 13, Torchwood and Caprica as well as YouTube hit Husbands, is repped by CAA and Hansen Jacobson.

Estrin counts ABC's recently canceled Zero Hour, The River, No Ordinary Family, The Good Guys and Prison Break among his credits. He's repped by WME and Ziffren Brittenham.

Should the Once spinoff not move forward, Espenson and Estrin will develop original projects for the studio under their overall deal.

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