Police said screams from Dee could be heard and she was covered in blood while Stratton repeatedly hit her with a fire extinguisher.
A barber and customer heard Dee banging and pleading "let me in" as the pair panicked and closed the door to a neighbouring salon.
Police said a customer opened the door when screams stopped and saw Stratton stab Dee in the chest with a knife.
The injured chef ran down Maitland Rd while the knife was still in her chest before collapsing outside a local shop.
Covered in blood, Stratton was arrested 1km from the cafe not long after the incident.
The 24-year-old has been charged with attempted murder and wounding a person with the intent of causing grievous bodily harm.
Dee was taken to hospital where the knife was removed during surgery. The Daily Telegraph reports she is in a serious but stable condition.
The Daily Telegraph said Stratton is a New Zealander who lives in the Newcastle suburb of Sandgate.
Stratton appeared in court today where his lawyer Mark Ramsland did not enter a plea or apply for bail on his behalf.
However, Ramsland's request for a psychiatric assessment to be conducted was approved.
"He wishes to express his regret and sadness for the incident," Ramsland said.
It's believed Statton and Dee were both new employees at the cafe.
Cafe owner Leya Aboltins thanked customers for their support on Wednesday night in a Facebook post.
"All the staff are completely shaken up and are struggling to come to terms with what happened," Aboltins said.
"Please keep my chef Ebony in your thoughts and prayers tonight as she is recovering in ICU.
Onyx will be closed until further notice.
Posted by Onyx Espresso Bar on Wednesday, May 12, 2021
"Myself, my staff, Onyx and most of all Ebony will take a long time to heal from the events of today.
"Please bear with us while we find our feet and make sense of it all."
Stratton will return to court on July 8.
