Fit a food processor with the metal blade or use a blender.
Turn on the machine, drop the green chilies and ginger through the feed cap, and mince.
Add 4 tbsp (2 oz / 60g) water, 1 tbsp (0. 5 oz / 15g) ground coriander, 1 tsp (0. 1 oz / 5g) turmeric, and 0. 5 tsp (0. 05 oz / 2g) paprika. Process until the mixture becomes a smooth, wet spice paste, then transfer it to a small cup.
Heat 4 tbsp (2 oz / 57g) of ghee or oil in a large nonstick saucepan over moderate heat. Carefully add the 11. 5 oz (325g) of paneer cheese cubes and fry them, constantly turning the pieces until they are evenly browned on all sides.
Remove the fried paneer with a slotted spoon and set aside.
In the same pan, add 1. 25 tsp (0. 1 oz / 3g) cumin seeds, 0. 5 tsp (0. 05 oz / 2g) black mustard seeds, and 0. 25 tsp (0. 02 oz / 1g) fennel seeds.
Fry the whole spices until the black mustard seeds pop and turn gray.
Add the remaining 4 tbsp (2 oz / 57g) of ghee or butter along with the blended wet spice paste.
Fry while stirring often until most of the water evaporates.
Stir in the 2 cups (16 oz / 450g) of peeled and diced tomatoes.
Continue to cook, stirring frequently, until the mixture reduces, becomes dry, and the oil distinctly separates from the tomato sauce (about 10 minutes).
Pour in 2. 5 cups (20 oz / 590g) of whey and bring the sauce to a rolling boil. If using fresh peas, add them now, reduce the heat to moderately low, cover, and cook for about 15 minutes until nearly tender.
Stir in the fried paneer cubes and the 1. 5 cups (10 oz / 285g) of defrosted frozen baby peas.
Simmer everything together on low heat for 5 minutes so the flavors meld and the cheese absorbs the sauce.
Stir in 1 tsp (0. 2 oz / 6g) salt, 0. 5 tbsp (0. 1 oz / 4g) garam masala, and your fresh coriander and mint right before you are ready to serve.
Don't Over-fry the Paneer: Fry the cheese cubes just until they achieve a light golden brown color. If you fry them too long, they will become rubbery. If your store-bought or homemade paneer feels a bit firm after frying, soaking the fried cubes in warm water for 10 minutes before adding them to the sauce will make them melt-in-your-mouth soft.
Let It Rest: Like many Indian curries, Matar Paneer tastes exponentially better if you let it sit for 1 to 2 hours after cooking. The fried paneer acts like a sponge, soaking up the vibrant mint, coriander, and tomato flavors as it rests.