Prep

Wash the moong dal and rice in several changes of water until the water runs clear. Place it in a bowl, cover with water, and soak for 2–3 hours.
Drain both the dal and rice after soaking. Place the soaked dal and rice in a wet grinder or blender along with green chillies, chopped ginger, curry leaves, asafoetida, turmeric powder, and salt. Grind to a smooth, fine paste, adding just enough water to keep the blades moving. Avoid adding too much water so the batter remains thick. Transfer the paste to a large mixing bowl.
Add the grated boiled potatoes, chopped onions, coriander, mint, sesame seeds, cumin seeds, sugar, and baking soda to the ground paste. Mix well so that all the ingredients are evenly distributed. If the batter feels too thick to spread, add a little water until it reaches a thick chutney-like consistency—spreadable but not runny.

Making the waffles

Preheat the waffle iron according to the manufacturer’s instructions. Lightly grease both plates with vegetable oil using a pastry brush or folded paper towel. Place a scoop of batter in the center of the hot waffle iron and gently spread it to fill the grid. Close the lid and cook until the waffles are golden brown and crisp. Avoid opening the lid too early to prevent the waffles from breaking. Mine took almost 12-13 minutes in my borosil waffle iron. It might take little less time in a heavy duty waffle maker.
Carefully remove the waffle using silicone tongs or a spatula. Repeat with the remaining batter, lightly greasing the plates before each batch. Serve the waffles hot, either plain or with plain yogurt on the side.