Heat the oil in a large, heavy pot, such as a Dutch oven over medium high heat. Add the cinnamon stick and cloves. When the cinnamon stick starts to unfurl, add the mustard seeds and cover the pot with a lid. When the seeds stop popping, add the cumin seeds and stir. After about 30 seconds, add the curry leaves--be careful, they will spit and sizzle!

Give that about 30 seconds and then add the onions with a pinch of salt. Toss occasionally, and let the onions caramelize to a golden brown. Add the garlic and ginger and keep caramelizing. Splash a tablespoon or two of water into the pan if the onions start to scorch or stick. Cook an additional 5 minutes.

Add the tomato paste, ground cumin, ground coriander, turmeric, paprika and 1 teaspoon of garam masala. Stir and let roast for 1 minute. Then add the tomatoes with another pinch of salt. Cook on medium high, stirring occasionally, for 10 minutes. When the tomatoes have thickened and deepened, add the chicken and potatoes with several pinches of salt. Toss for 1 minute and add the zucchini and chickpeas with liquid--if the curry needs even more liquid add more stock or water. Bring to a boil, then reduce the heat and let simmer for 10 minutes.

Add the spinach--I do not bother defrosting or drying, as that frozen spinach water is just going to add flavor and vitamins to the curry. Once the spinach has melted into the curry, add the cilantro, return to a simmer, cover, and let simmer gently for up to an hour before serving.

Before serving, whisk 1 cup of the curry into the sour cream or yogurt. When it is warmed through, add it back into the curry. Turn off the heat. Then add 1 tablespoon of garam masala and the lemon/lime juice. Taste for salt, more garam masala or more lemon/lime juice. Serve with Basmati rice or flatbread.