In a mixing bowl, combine 1.5 cups of small-grain rice, ½ cup of urad dal, and ½ tsp of methi dana (fenugreek seeds). Wash and soak this mixture for 4-5 hours. Drain the soaking water and set it aside; you'll use some of this water while grinding the batter. Also, wash and soak ½ cup of poha (flattened rice).
Next, place the soaked grains, soaked poha, and some water into a blender. Grind the mixture into a smooth batter with a ribbon-like consistency. Transfer the batter to a mixing bowl.
In a pressure cooker, whisk the batter in one direction (refer to the video). Cover the cooker with a lid and keep the batter in a warm place to ferment. After 8 hours, the batter should be properly fermented.
Now, add salt, hing (asafoetida), and 1 tbsp of sugar to the fermented batter. Mix these ingredients well.
In a tadka pan, mix 2 tbsp of water and 2 tbsp of oil, and heat the mixture. Add ¼ tsp of baking soda and mix well. Incorporate this mixture into the batter; the baking soda gets activated in the hot oil and water mixture.
Set aside a portion of the batter for the middle chutney layer.
To make sandwich dhokla, pour 2 cups of the dhokla batter into a greased mold. Steam the first layer of dhokla in a pre-heated cooker for 5 minutes on high flame, without placing the whistle on the lid.
Meanwhile, prepare the green chutney. In a blender, combine 1 cup of coriander leaves, 4-5 green chillies, 1-inch piece of ginger, 1 tbsp of peanuts, ¼ tsp of cumin seeds, 1 tsp of lemon juice, 1 tbsp of sugar, salt to taste, some ice cubes, and water. Blend the ingredients into a thick paste. Set aside the green chutney.
Mix 3-4 tbsp of the green chutney into 1 cup of batter. Once the first layer of dhokla is steamed, spread this chutney layer on it. Steam the chutney layer for an additional 5 minutes on high flame.
Now, spread 2 cups of dhokla batter on top of the chutney layer. Sprinkle some black pepper powder over it. Cover and steam the dhokla for 15 minutes on medium-high flame.
Once the dhokla is properly steamed, remove it from the steamer and allow it to cool completely. De-mold the sandwich dhokla and cut it into pieces.
For the tempering, heat oil in a pan and add mustard seeds, white sesame seeds, hing, curry leaves, and chopped green chillies. Sauté for a minute and then pour this tempering over the dhokla.
Your sandwich dhokla is now ready to be served with the prepared chutney.