To make the curry, heat a large pot or Dutch oven over medium high heat. Add the grapeseed oil with the mustard seeds and cover the pot. Let the seeds pop--when they slow down, add the urad dal and stir. Roast for a minute or so and then add the cumin seeds and curry leaves (be careful--the curry leaves will splatter!). Continue stirring and let roast until the cumin seeds and urad dal are a shade or 2 darker and fragrant. Do not let the cumin seeds burn.

Add the onions with a pinch of salt. Toss into the spices and caramelize for about 20 minutes, stirring occasionally. If the onions start to scorch or stick, add about a quarter cup of water and let it cook off, scraping the pan clean. When the onions are brown, add the ginger, garlic, turmeric, paprika, ground coriander, cumin and amchur powder. Add another pinch of salt. Cook for 2-3 minutes, stirring often.

Add the tomatoes, mangoes and tamarind concentrate. Stir into the onions and bring to a simmer. Cook for 10 minutes, to concentrate flavors. Add the cooked chickpeas with their cooking liquid and aromatics. Add the spinach (I don't even bother defrosting) and cilantro. Stir into the vegetables until the spinach is defrosted and mixed into the curry. Bring to a simmer and let simmer quite gently for at least 20 minutes and up to 2 hours. Before serving, add 2 tablespoons of garam masala and the juice of 1 lime. Check for more salt, lime juice or garam masala.

Serve with flatbread or basmati rice, and a dollop of plain Greek yogurt. I also serve with red chile pepper flakes on the side for those who like things hot.