From left: Julia Roberts, Ewan McGregor and Meryl Streep in August: Osage County
09/11/2013 AT 11:25 AM EDT
Working with Meryl Streep is a dream come true for any actress – and Julia Roberts
is no exception.
But Roberts, 45, admits her longtime fantasy never involved butt pads, flop sweat and a chokehold.
Still, that proved to be their reality when Roberts was cast to play Streep's eldest daughter in August: Osage County
, the film version of Tracy Letts's 2008 Tony-winning best play about a dysfunctional Oklahoma family gathered around their sharp-tongued, eccentric dying mother, played by Streep, 64.
"It was intimidating, certainly, to be in these scenes with her, choking her, things like that," Roberts admitted at Tuesday's Toronto International Film Festival press conference for the movie. "That's not how I pictured it going in my mind all these years when I thought we'd be together, drinking tea together and speaking in fabulous accents and dressed up and looking very chic."
Her projection strayed from the reality, however. "And instead there I am sweating and wearing a big butt pad," she added. "So that's not how it was in my dream."
Not that this was in any way a disappointment.
"It was the best acting experience in my life," Roberts declared. "Our experience was a treasure box of discovery for me. And at the top of the heap was ... Meryl Streep, who showed that it is about working hard. Because I've never seen anybody work harder than she works. She doesn't just snap her fingers and be a genius. She really is just the hardest working girl in the room. I was so grateful to see that up close."
Yet despite her passion for the film, Roberts, mother of twins
Hazel and Phinnaeus, 8, and son Henry
, 6, said family trumps the trappings of fame every time.
"Family values, that's values in general," she responded when asked whether family or fame is more important. "That's all there is. Fame is a summer breeze that comes and goes. But to have a bedrock of knowing who you are, that's what it's all about."