Soak the rice and urid dal separately for at least 8 hours in plenty of water.
Drain , then grind to a paste in a blender, adding water or whey as required to make a thick batter.
Mix the batters together, add salt and any spices as desired then leave to ferment in a warm place for at least 8 hours*
Place a medium non stick pan over high heat and add 1 tsp of oil. Add the sliced mushrooms and sauté for a few minutes. Add a big handful of spinach and quickly wilt. Season with salt and pepper then transfer to a container to keep warm
Return the pan to the heat and add 1 tsp of oil, swirling to coat the base of the pan
Stir the batter and pour a ladelful into the middle of the pan.
Spread the mixture quickly, then pour a few drops of oil around the edges. Let it cook until tiny holes appear on the surface. Pile the mushrooms and spinach onto one half of the dosa, then crack in 2 eggs on the other half.
Place a lid on the pan and cook for 3 or 4 minutes until the egg whites are set.
Carefully, lift the dosa from the pan with a fish slice and place on serving plate.
Sprinkle with chilli flakes and chilli sauce if desired.