A female ex-con spent nearly two years in prison for robbing an Upper West Side bank — and then got busted again this month for hitting the same location when a teller recognized her, authorities say.

Herlene Lawton, 64, wasn’t even out of the pokey two months for the 2013 heist when she hobbled into the Santander Bank at Broadway and 103rd Street on crutches Sept. 9 and allegedly demanded dough.

She then fled in a getaway car — a yellow taxi she hailed on the street — but was soon caught, thanks to the sharp-eyed teller, law-enforcement sources said.

Lawton’s obsession with the financial institution began June 24, 2013, when she passed a note to the then-Sovereign Bank teller that read, “I want $1,000,’’ authorities said.

“I have a gun,’’ she hissed to the worker, according to a criminal complaint. “I don’t want to blow your head off.’’

Just two hours after making off with $1,000 in cash, Lawton was caught by cops and eventually sent to prison in December 2013. She did her time and was released this past July 20.

But the itch to knock over the same bank location, now a Santander branch, for a second time proved too much for Lawton — and she robbed it again nearly two weeks ago, officials said.

Lawton passed a note to the teller and told her, “Gimme the cash. I know I’m going to get caught. Don’t make me blast you. I have a gun,” according to the complaint.

The teller handed over a bag containing $1,020 and a dye pack.

Lawton ditched her crutches outside the bank and fled northbound on Broadway, where the dye pack exploded and caused her to drop the bag of loot, according to cops. She then hailed a cab and took off in an unknown direction.

Sources said a teller who remembered Lawton from the first heist helped identify her when cops arrived. She was nabbed later that night and charged with first-degree robbery, according to police.

Lawton has more than 30 prior arrests and has spent much of her time behind bars since 2004, mostly for drug-related offenses, cops said.

Nearly a year before being busted for her first Upper West Side bank robbery, Lawton was serving an eight-year sentence for the criminal sale of a controlled substance, according to records.

She is currently being held at the Elmurst Hospital Prison Ward in Queens for psychiatric evaluation.

“She’s a lunatic,” said a law-enforcement source. “That’s basically what it all boils down to.”