In a wide mixing bowl, whisk 155 g yogurt with the marinade spices until completely combined.
Melt 66 g ghee in a large heavy pot over medium heat. Add the whole spice and fry for 1 minute until fragrant and crackling.
Tumble in 150 g chopped onion and sauté for 5 minutes until pale golden. Add the ginger and garlic pastes and fry for 2 to 3 minutes until the onions turn rich golden brown.
Take the pan off the flame and whisk in the spiced yogurt. Return to the heat and cook, stirring, for 2 to 3 minutes until the ghee separates and floats to the top.
Tip in 150 g puréed tomato and 1200 g potato chips. Fry for 2 to 3 minutes until the fat separates out once again.
Pour in 1 litre water and add salt to taste. Bring the liquid to a rolling boil, drop the heat to low, and simmer for 10 minutes, stirring occasionally, until the potatoes are three-quarters done.
Stir in 250 g urad dal vadi and bring back to the boil. Lower the heat and simmer for another 10 minutes, stirring frequently, until the potatoes are cooked through and the gravy is light and fluid.
Stir through the finishing spice, then remove from the heat. Check the seasoning, add more salt if needed, and scatter over 1 g chopped coriander leaf.
Use 120% of the weight; melt gently over low heat to avoid burning the milk solids, which will yield a softer, creamier richness rather than a nutty aroma.
Use 80% of the weight, finely shredded and browned slowly with a pinch of asafoetida. Replicates the bulk and natural sweetness in gravies without allium.
Use 40% to 50% of the fresh tomato weight mixed with a splash of water. Imparts a deeper red colour, thicker sauce, and slightly sweeter cooked flavour.
Grind whole seeds finely in a spice grinder; use equal weight (1:1). Ensure it cooks through gently, as undercooked or burnt ground seeds become intensely bitter.
Crush dried leaves between your palms and add towards the end; use 50% of the weight. Gives the unmistakable maple-herb aroma without the sharp bitterness of the seeds.
Use 50% of the weight and stir in near the end of cooking. Adds warmth and depth since it contains ground coriander, but introduces stronger spices like clove and cinnamon.
Steep a tiny pinch (0.1 g per 2 g turmeric) in 2 tbsp warm water; use to match the rich golden hue. Contributes an aristocratic, honeyed floral flavour rather than earthy bitterness.