Pick the methi leaves from the thick stems (tender stems are fine). Wash in 2 to 3 changes of water, drain well and chop finely.
To reduce bitterness, rub the chopped methi with 1/2 tsp salt, leave it for 10 minutes, then squeeze out the green water with your hands and discard it.
Heat the oil in a heavy pot on medium heat. Add the cumin seeds and let them sizzle, then add the onion and fry until light golden, about 5 minutes.
Add the ginger garlic paste and green chillies and fry for 1 minute until the raw smell goes.
Add the tomatoes, red chilli powder, turmeric, coriander powder and salt. Cook, stirring, until the tomatoes soften and the oil starts to separate, about 5 to 6 minutes.
Add the potatoes and carrots and stir to coat them in the masala. Add 1/2 cup water, cover and cook on low heat for 10 to 12 minutes until the potatoes are nearly soft.
Add the peas and the squeezed methi. Stir gently, cover and cook for 7 to 8 minutes until the methi is soft and the peas are cooked.
Uncover and cook on medium-high heat for 4 to 5 minutes, stirring gently without breaking the potatoes, until the extra moisture dries up and you see oil at the edges (bhunai).
Sprinkle the garam masala and fresh coriander and cook for 1 more minute. Turn off the heat.
Transfer to a serving plate and put the white butter on top so it melts into the hot sabzi. Serve with hot roti, paratha or plain rice.
