Place the cashews in a bowl and cover with ⅔ cup (160ml / 5.4 fl oz) of freshly boiled water.
Let them soak for at least 10 minutes to soften.
Meanwhile, prepare the fenugreek. Wash the leaves thoroughly, then trim off and discard the tough lower stalks. Finely chop the leaves and place them in a large bowl of cold water with a generous pinch of salt.
Let them soak for 10 minutes to reduce bitterness, then drain well.
Transfer the soaked cashews and their soaking water to a blender.
Add the peeled ginger and green chiles, and blend until you have a completely smooth paste.
Melt the butter in a large lidded frying pan or skillet over medium heat.
Add the chopped tomatoes and cook for about 5 minutes, stirring occasionally, until they soften and break down.
Stir in the garam masala, mango powder, sugar, and 1¼ teaspoons of salt.
Add the drained fenugreek leaves to the pan.
Cover with the lid and cook for 6-8 minutes, until the leaves are tender and wilted.
Pour the cashew paste into the pan and cook for 2 minutes, stirring constantly to prevent it from sticking.
Stir in the light cream and the frozen peas.
Cover the pan again and let it simmer for another 5 minutes, or until the peas are cooked through and the gravy has thickened slightly.
Taste and adjust the seasoning if needed.
Serve hot with fresh naan, roti, or steamed basmati rice.
Don't skip soaking the fenugreek leaves in salt water; it's the key to mellowing their natural bitterness for a perfectly balanced curry.
Using 1 ½ cups (400g / 14.1 oz) of canned crushed tomatoes is a great time-saver and helps create a consistently smooth gravy.
Adjust the spice level by de-seeding the green chiles for a milder flavor, or add an extra one if you enjoy more heat.
