Heat the 6 tbsp (90 ml) ghee or 2 tbsp (30 ml) oil in a heavy 3-quart (3-liter) nonstick pan over moderate heat.
Add the 1 tsp (5 ml) mustard seeds, ginger, and chilies to the fat; fry until the seeds sputter and turn gray.
Sprinkle in the 0. 25 tsp (1 ml) asafetida and curry leaves, then stir in the 20 oz (570 g) of cubed potatoes within 5 seconds.
Fry the potatoes for 2–3 minutes while tossing with a wooden spoon (add the 4 tbsp/60 ml butter now if you started with oil).
Add the 16 oz (455 g) of eggplant, spinach, stock, turmeric, zest, juice, cinnamon, cloves, fennel, nutmeg, and 1. 25 tsp (6 ml) salt.
Bring the mixture to a boil, then reduce heat to low and partially cover to cook for approximately 30 minutes.
Monitor the pan occasionally to ensure the Baigan Aloo Charchari isn't drying out too fast; add a splash of water if needed.
Once the vegetables are fork-tender and the liquid is fully absorbed, allow them to sizzle in the remaining ghee.
Increase the heat to moderately high and fry the vegetables without stirring until a charred crust forms on the bottom.
Gently fold the charred crust back into the soft vegetables just before removing from the heat to serve.