Wiktionary
muffin cap
n. 1 A style of close-fitting cap or hat worn by women in the 16th century and later; a caul. 2 A low, loose cap resembling a beret, but with a brim that goes all the way around the head; popularized in the 19th century as a hat for children, especially in the lower classes.
Usage examples of "muffin cap".
The heavyset woman, her dark hair tucked up into a clean muffin cap, looked him over with a practiced eye.