Bring 3-4 cups of water to a boil and then turn off heat. Soak spinach leaves in the boiled water for five minutes.
Take out the spinach leaves from hot water and soak them in cold water to stop further cooking. (This helps in retaining the green color of the leaves.)
Blend the leaves to a fine purée using a mixer.
Bring 3-4 cups of water to a boil and then turn off heat. (You can use the same water which was used to blanch spinach but mushrooms might turn slightly green.)
Add salt and 1 tbsp lemon juice, stir, and then add sliced mushrooms.
Allow the mushrooms to soak for five minutes and then drain the water.
Heat oil in a kadai and add chopped onion.
Sauté onion on medium flame for a minute or so and then add ginger-garlic paste. (Usually I grate ginger and 3-4 cloves of garlic to make this paste. It's tough to make this paste in mixer for such small quantity, and I don't make it in bulk as I don't use it all that much in daily cooking.)
Add chopped green chili. (You can omit this step if your kid doesn't eat hot food. I have stopped adding green chili since Devansh started eating this sabzi.)
Sauté till onion turns light brown and then add chopped tomato.
Add red chili powder and sauté till the oil starts to separate from the mixture. (Again, moms of younger kids can avoid adding red chili powder; I don't add it.)
Turn off heat, allow the mixture to cool, and then blend it to a smooth paste in a mixer.
Transfer the paste to a kadai and turn on heat.
Add puréed spinach and mix properly with the paste.
Add blanched mushroom slices and mix properly with spinach.
Add garam masala and salt after a couple of minutes, and give the sabzi a good stir.
Cook on medium flame for five minutes while stirring intermittently and then turn off heat. (Don't cover the kadai while the sabzi's cooking.)
Add 1 tbsp lemon juice and stir once. (You should add lemon juice in spinach as vitamin C helps absorb iron in spinach (non-heme iron) properly.)
Serve hot with chapatis.