Duchniak’s on Kirkgate was targeted overnight between Sunday and Monday, March 25, when the thieves smashed the window to the front door to gain access.
They took off with the till which only contained a limited amount of change.
Aneta Duchniak, who runs the popular restaurant, said: “I had a call from the police to say the restaurant had been broken into.
“They only took the register, although there was a lot of expensive champagne they could have taken.
“We’d been hosting a celebration the night before we and we had been very busy, there was about 40 people in.
“Maybe somebody had been watching.
“A woman who lives across the road at Primrose House said she heard a loud bang at 3.30am but we were told by police that someone had entered after 6am.”
It is not certain if somebody had tried to smash the glass and enter but had failed, and an opportunist had later managed to gain access to the premises and get away with the till.
It is the second time the restaurant has fallen victims to burglars following a break-in in November 2017.
Mrs Duchniak said she would not be deterred and is now considering putting bars across the windows to help improve security.
Anyone with information is being asked to contact police on the non-emergency number 101 and quote crime reference number 13190153558.