Homestyle Dosas with Tomato Chutney

Ingredients:
2 cups long-grain white rice
½ cup whole or split urad dal (black gram)
½ tsp. fenugreek seeds
1 tsp. kosher salt
2 tsp. plus 2 Tbsp. vegetable oil
1 small onion, finely chopped
2–3 small green chiles (such as serrano), seeds removed if desired, finely chopped
4 small tomatoes or canned whole peeled tomatoes, chopped
Kosher salt
2 tsp. black mustard seeds
8–10 fresh or frozen curry leaves
1 dried red chile (such as bird or chile de árbol)
1 tsp. split or whole urad dal (black gram)
A pinch of asafoetida (optional)
1 tsp. ghee or clarified butter
melted
divided
plus more for griddle

Instructions:
The morning before you make your batter, rinse rice in a fine-mesh sieve under cold running water, until water runs almost clear. Transfer to a large bowl and cover with 4 cups cold water. If your tap water is heavily chlorinated, use filtered water for soaking as chlorine will inhibit fermentation later on.
Pick over dal for debris, then rinse in sieve under cold running water. Transfer to a medium bowl and add fenugreek. Cover with 2 cups cold water (again using filtered if needed). Let rice and dal soak at least 8 hours and up to 10 hours.
Drain rice, holding back grains with your hand and pouring off most of the soaking liquid into a pitcher or large measuring glass. Transfer rice to a blender. Pulse to get things going, then purée, sparingly adding soaking liquid as needed, until a paste forms (mixture should be foamy and still slightly gritty when rubbed between your fingers). Pour into a clean large bowl. Repeat process with dal mixture, then vigorously stir blended dal into rice paste.
Add reserved soaking liquid as needed to create a pourable batter that falls off the spoon in a steady stream and gradually dissolves into itself. Stir in salt. (If you are in a warm climate, add salt after fermentation to keep batter from becoming overly sour.) Cover bowl with a kitchen towel, then a silicone lid (this will keep the surface of the batter from drying out). Set bowl in a warm spot (a proofing box or an oven with the light on and a bowl of hot water placed inside work well). Let batter sit until airy and pleasantly sour (when you drizzle it from a spoon, it should fall on itself in slowly dissolving ribbons), 4–6 hours in a very warm environment and as long as 2 days in a very cool environment. In general, 14 hours is a safe starting point.
Do ahead: Batter can be made 1 week ahead. Once fermented, cover and chill. Bring to room temperature before cooking. Thin with water if needed to reach a thick but pourable consistency.
Heat 2 tsp. oil in a medium skillet over medium. Cook onion, stirring occasionally, until translucent, about 3 minutes. Add green chiles and cook, stirring, 1 minute. Reduce heat to low, add tomatoes and any juices and a generous pinch of salt. Cook, stirring often, until tomatoes are tender, 7–9 minutes. Carefully transfer to clean blender or a food processor and blend until smooth; reserve skillet. Taste chutney and season with more salt if needed. Transfer to a small bowl.
Wipe out reserved skillet and heat remaining 2 Tbsp. oil in skillet over medium. Cook mustard seeds, stirring constantly, until they start to pop, about 30 seconds. Add curry leaves, dried red chile, and dal and cook, stirring occasionally, until curry leaves wilt and crisp and dal is starting to brown, about 2 minutes. Mix in asafoetida, if using, and remove spice oil from heat. Mix into chutney.
To cook dosas, heat a griddle or large skillet (the larger the better; you want the batter to have room to spread) over medium. Sprinkle a little water on surface; if it sizzles you’re good to go. (It’s important though not to let griddle get hotter than medium. If it’s too hot, the batter will start to cook before it’s fully spread out, yielding a thick dosa, or worse, a thin dosa that tears. Adjust heat as needed). Brush griddle with a thin layer of ghee, wiping off excess with a folded paper towel. Ladle a generous ⅓-cupful of batter in the center of griddle and use ladle to spread batter, working outward in continuous circles and never lifting ladle off surface, to create an 8"-diameter round. Ridges of thick and thin batter will form naturally. Cook dosa 30 seconds, then drizzle ⅛ tsp. ghee over batter. For a spongier dosa, cover with a large bowl and steam until cooked through, about 2 minutes (cooked underside should show through thinner spots, and thicker spots should be opaque and bouncy). For a drier dosa, cook until surface is mostly set, about 2 minutes, then, using a fish spatula or other wide spatula, flip dosa over (it should easily lift from the griddle at this point) and cook until second side is lightly golden, about 20 seconds. Fold dosa in half so toasted side is facing out and transfer to a plate. Repeat process with remaining batter and ghee.
Serve dosas as they are ready with chutney alongside for dipping.