The 'Roar' singer and Girls actress Allison were seen leaving lunch at Sant Ambroeus Restaurant on New York's Upper East Side on Tuesday afternoon (17 December).
Earlier that day, Katy had appeared alongside boyfriend John Mayer for their first ever joint TV interview on Good Morning America to promote their duet 'Who You Love'.
But she swapped the glam figure-hugging dress and sky high heels she wore on screen for something a little more casual for her lunch date.
Wrapping up warm against the Manhattan chill, the star layered a black coat over skinny jeans and cosy UGG boots. She added a knit hat and chunky scarf for extra warmth.
Katy and Allison are thought to have met via their boyfriends last year (Allison is dating Ricky Van Veen, the co-founder of College Humour website) and have been firm friends ever since - Katy even brought Allison as her date to The Grammy Awards.
"She's the hottest date," Allison told US show Anderson at the time. "She's a friend of mine and she's nominated as she should be. I can't wait to go. Obviously she's awesome. She's the best."
As quite big fans of Katy, we'd probably agree.
Watch Katy and John getting romantic in their 'Who You Love' video: