Take dosa batter in a bowl. Add semolina and sugar. Mix well and keep aside for 10-15 mins. Add salt, if needed.
Add 1/4 tsp cooking soda and give a good mix.
Semolina absorbs water. If the batter is thick, add a few tablespoons of water and adjust the consistency. The batter should be thick but pourable consistency.
Chop the veggies and keep them ready.
Heat the dosa pan/tawa over a high flame. When hot add 1 tablespoon of oil in the middle and rub a half-cut onion all over the pan.
Turn the flame to medium and pour two scoops of dosa batter in the center of the hot pan.
To make thick uttapam, let the batter spread on its own. For thin uttapam, swirl the batter once.
You will start seeing air bubbles form in the middle and the sides.
Lower the heat to low and spread the toppings all over the uttapam.
Pour oil over the topping and around the edges.
The top batter will cook and start to look dry. Turn the flame to medium, carefully lift the uttapam with a thin silicone spatula or stainless steel turner and flip it over.
Cook for 1 to 2 minutes as the veggies start to caramelize. Regulate the flame from medium to low to prevent toppings from burning.
Flip again.
Uttapam is ready. Transfer it to a plate and serve with chutney or sambar.