Karma N. Kargl, 34, of 199 Schneck Ave. in Westbury, was arrested, police said, and was charged with first-degree robbery, and fourth-degree criminal possession of a weapon.
Kargl entered the store at 4220 Hempstead Tpke. about 2:30 p.m., Nassau police said, and after taking a box of Entenmann's Bakery doughnuts from a display, brought them up to the counter as if to make a purchase.
But there, she displayed a knife, police said, and demanded money from the sales clerk. The clerk backed off, and headed away from the counter and into a storage room without giving her any of cash, police said.
Kargl then took the box of doughnuts and left the store, police said, driving off in a blue sedan whose license plate was recorded by witnesses.
She was later arrested at her home, police said, and was to be held for arraignment Tuesday morning in First District Court, Hempstead.
No information was released by police as to whether any of the stolen doughnuts were recovered.