Boil the potatoes. Peel them after they cool down. Grate and keep aside.
Boil the other vegetables and mash them slightly by hand.
In a frying pan or tawa, add 1 tablespoon oil and 2 tablespoon butter and fry the onions till they turn pinkish.
Add ginger-garlic paste and mix.
Now add tomatoes and fry till tomatoes become mushy.
Add all the spice powders and mix properly.
Pour the mashed potatoes and the mashed vegetables. Mix properly.
Add 1/2 cup water. If needed, add more water.
Keep on mixing and mashing the vegetables on the tawa with the pav bhaji masher.
Add salt to taste.
Keep the lid covered and let it cook for some time.
After 5 minutes switch off the gas.
Garnish it with a blob of butter and coriander leaves.
Slit the pav. Apply butter and fry the pav on both sides.
Serve the hot Bombay pav bhaji with fried pav, chopped onions and a piece of lemon.