Make the tempering: Heat 1 tablespoon oil in a small pan. Add mustard seeds and let them crackle. Add cumin seeds, curry leaves, green chili, and hing. Fry for 20 seconds until fragrant. Turn off the heat and let it cool slightly.
Prepare the batter: In a large bowl, add rava, yogurt, salt, and the prepared tempering (with oil). Mix well.
Add water gradually: Pour water little by little, whisking continuously to avoid lumps. The batter should be slightly thick, like pancake batter. Not too thin.
Rest the batter: Cover and let it sit for 15-20 minutes. The rava will absorb water and soften. Check consistency after resting and add a tablespoon or two of water if it has thickened too much.
Heat the pan: Place a non-stick or cast iron tawa on medium heat. Grease it lightly with oil.
Add eno: Just before making the first uttapam, add eno fruit salt to the batter and stir gently. You will see bubbles forming immediately.
Pour and spread: Pour a ladleful of batter in the center of the hot tawa. Gently spread it in circular motions with the back of the ladle to form a thick pancake, about 1/4 inch thick.
Add toppings: Immediately sprinkle chopped onions, tomatoes, capsicum, coriander, and green chili evenly on top. Press them gently into the batter with the back of the ladle.
Drizzle oil: Add 1/2 to 1 teaspoon oil around the edges of the uttapam and a few drops on top of the vegetables.
Cover and cook: Cover with a lid and cook on medium flame for 3-4 minutes. The uttapam will cook from the steam, and the vegetables will soften.
Check and flip (optional): Lift the edge to check if the bottom is golden and crisp. You can flip it for 30 seconds on the vegetable side if you prefer, but traditionally it is not flipped.
Serve hot: Remove from the tawa and serve immediately with coconut chutney or sambar.
Notes
Batter thickness: The resting time absorbs water, so always check and adjust before adding eno.
Eno timing: Add eno only when the pan is hot and you are ready to cook. It loses effectiveness if mixed too early.
Pan heat: Medium flame is important. Too hot and the base burns, too low and it becomes soggy.
Make-ahead: You can prep the batter (without eno) and refrigerate for up to 6 hours. Bring to room temperature, adjust consistency, and add eno before cooking.
Tawa choice: Non-stick works best for beginners. Cast iron gives better crispiness but needs good seasoning.
Vegetable moisture: Pat tomatoes with a paper towel if they are too juicy. Excess moisture makes the uttapam soggy.
Batch cooking: Keep cooked uttapams warm in a casserole or low oven while you finish the batch.