When they begin to sizzle add the onion. Cook on medium heat till onion is brown. Then add the ginger garlic paste and stir for about 45 seconds. Pour in the tomato puree and sprinkle the coriander, cumin, turmeric and chili powders.
Bring to a boil. Then reduce heat to a simmer, and let the gravy cook for about 12 minutes or till it thickens and oil floats on top. (Canned tomato puree will cook in lesser time). If the sauce gets too thick add ½ cup water whenever needed.
While the sauce is cooking, work on the mushrooms. Wipe the mushrooms clean with a paper towel. If the mushrooms are large, cut them in half, if not leave them whole. Mix together the mushrooms, pepper, turmeric, chili powder, and yogurt and set side.
Heat a large skillet and add oil. When the oil is hot, add the mushrooms/ pepper mix. Make sure you don’t crowd the pan; do this in batches if needed. Cook the mushroom and peppers on medium heat, till they start to brown a little. Don’t move the mushrooms around too much, they wont brown.
When the tomato sauce is done, add the sautéed mushrooms and bell peppers to it. Also add kasoori methi(or celery leaves and fenugreek) and salt to taste. Cook on medium heat for about 3 minutes or till the peppers are cooked. Turn off heat and stir in heavy cream if using. Garnish with chopped cilantro.