The dosa is the foundational fermented rice-and-lentil crepe of South India: a thin, crisp, faintly sour disc cooked on a flat griddle and used as a base for an enormous family of fillings. Its reputation rests on two things working at once, the depth of flavor that fermentation builds into the batter and the cook's control of a hot tawa. The angle here is the batter itself, because everything stacked on top of a dosa lives or dies on whether the crepe under it is correctly soured, correctly thinned, and correctly crisped.
The build starts well before the griddle. Raw rice and skinned black gram lentils are soaked separately, ground to a smooth slurry, combined with a little salt, and left to ferment overnight until the batter rises, smells tangy, and carries fine bubbles. To cook one, a ladle of batter is poured onto a hot, lightly greased tawa and spread outward in a fast spiral from the center to a wide, even circle. Oil or ghee is drizzled around the rim, the surface is left untouched until it sets and lifts, and the crepe is folded or rolled off the heat. Good execution shows a sheet that is lacy and crisp at the edge, cooked through but never leathery, with a clean sour note from real fermentation and a surface that releases cleanly without tearing. Sloppy execution comes from underfermented batter that tastes flat and raw, a tawa too cool to set the surface so the crepe goes pale and rubbery, batter spread too thick so the center stays gummy, or a griddle so dry the disc sticks and shreds when lifted.
The dosa shifts more than almost any other item in the South Indian repertoire. The plain version is served folded with chutney and sambar and judged purely on crispness and sourness. Thinning the batter and adding rice flour gives the brittle, glassy lace of a rava style; a spiced potato mound folded inside makes the masala form; a smear of red garlic chutney across the surface turns it into a Mysore-style version. Each of those is a distinct preparation that deserves its own article rather than being crowded in here. Across all of them the constant is the same, fermented batter and a properly governed griddle, and no filling or accompaniment salvages a pale, sour-less, gummy crepe.