The ring shape isn't decorative — vendors punch a hole in the center so the dense urad dal batter fries evenly all the way through instead of staying doughy in the middle.
Urad dal is ground into a thick batter, whipped until light, shaped by hand into a ring, and deep-fried until the outside turns deep golden and crackly while the inside stays soft. Tamil Nadu's tea stalls and 'military hotels' serve it hot with coconut chutney and sambar, often alongside filter coffee.