Soak the Rice and Lentils: Clean and wash the rice, chana dal, toor dal, and white urad dal thoroughly, then soak them together in water for 6–8 hours.
Grind the Soaked Mixture: Drain and discard the soaking water, then transfer the soaked rice and lentils to a grinder or blender and grind until coarse. Do not process the mixture into a smooth batter, as the coarse texture is important to the handvo. Combine with Yogurt: Transfer the coarse rice-lentil mixture to a large bowl or pan, add the sour yogurt, and mix thoroughly until evenly combined.
Ferment the Batter: Place the covered batter in a warm area at approximately 25°C and leave it to ferment for at least 8 hours. The batter should rise to nearly double its original size. Preheat the Oven: When ready to prepare the handvo, preheat the oven to gas mark 4, 170°C/320°F.
Add the Spices and Vegetables: Add the grated dudhi, red chilli powder, turmeric powder, ground cumin-coriander powder, crushed green chillies, crushed ginger, sugar, fresh coriander leaves, and methi achar masala to the fermented batter. Mix well until the ingredients are evenly distributed.
Adjust the Batter: If the batter is too thick to work with, add a few tablespoons of water and mix until it reaches a suitable consistency.
Prepare the Vaghar: Heat the oil in a small pan, then add the mustard seeds, cumin seeds, cinnamon bark, cloves, and hing. Once the seeds begin to crackle, add the curry leaves and remove the tempering from the heat. Combine the Tempering: Pour a few spoonfuls of the prepared vaghar into the baking tin, then mix half of the remaining vaghar into the handvo batter.
Activate the Batter: Add the bicarbonate of soda or Eno and the lemon juice to the batter, then mix gently without overmixing.
Fill the Baking Tin: Pour the prepared handvo batter into the baking tin, then spread the remaining vaghar over the surface.
Add the Sesame Topping: Sprinkle the sesame seeds generously over the top of the batter.
Bake the Handvo: Bake in the preheated oven for 45–50 minutes, or until a skewer inserted into the center comes out clean.
Rest Before Cutting: Leave the baked handvo in the tin for 10–12 minutes so it can settle before cutting it into pieces.