Step 1Prepare the chicken: Bring ¾ cup water to a boil. Pour ½ cup into a small bowl and stir in the tomato paste until dissolved. Place the saffron threads in a small mortar and pestle and grind to a fine powder. Transfer to a small bowl and add 2 tablespoons of the just-boiled water. Reserve both bowls and the remaining boiled water.
Step 2Heat the olive oil in a large saucepan over medium heat. Add the onion, sprinkle with a small pinch of salt, and cook, stirring occasionally, until golden, 8 to 10 minutes. It’s OK if the onion takes on some color. Add the green beans and 1 ½ teaspoons salt, and cook, stirring occasionally, until the green beans soften slightly, 6 to 8 minutes. If the pan gets too dry, drizzle in more olive oil. Take care not to burn the green beans but also take care that the beans maintain their shape and do not turn soft and mushy.
Step 3Add the chicken, turmeric, cumin, cinnamon, pepper and 1 ½ teaspoons salt. Cook, stirring occasionally, until the chicken takes on a little color, about 3 minutes. Add the lemon juice and reserved tomato-paste water and saffron water. There’s most likely saffron clinging to the sides of your bowl. Drizzle in a little of the reserved 2 tablespoons water, swish it around and add to the mixture. This is precious stuff. Stir everything to combine. Reduce the heat to medium-low and cook at a gentle simmer until the chicken and green beans are just cooked through and all the flavors come to life, about 15 minutes. Taste to make it delicious. More salt? A little more lemon juice? The mix should be juicy but not too runny because it will get combined with the rice. Remove from the heat and partially cover until ready to mix with the rice.
Step 4While the chicken simmers, prepare the rice: Place the rice, olive oil, salt, and 1 ½ cups water in the bowl of a 5-cup Persian rice cooker. Give it a gentle stir with a wooden spoon, cover, and turn on the cooker to max/60 minutes. Once all the water has been absorbed (it’s OK to lift the lid to check), around the 30-minute mark, unplug the rice cooker to pause the cooking. Gently scoop out the rice in the center into a wide bowl without disturbing the bottom layer (this is the tahdig), leaving a 1-inch-thick layer of rice against the bottom and around the sides. Gently fold the chicken mix into the rice in the wide bowl and return to the rice pot one spoonful at a time with care, so that the rice grains don’t break and turn mushy. It might seem like there is more mix than rice, but don’t worry, the rice will expand in the second phase of cooking.
Step 5Wrap the lid of the rice pot with a clean kitchen towel or a couple of layers of paper towels to catch the condensation. Place the lid firmly back on and plug the rice cooker back in. When the cooker timer goes off and the rice is done, unplug the cooker. Wearing oven mitts, place a platter larger than the rice cooker bowl over the bowl insert. Lift the bowl out and quickly and confidently flip the bowl and platter together. Lift off the bowl slowly to reveal the tahdig on top. There may be darker spots in the tahdig from the tomato paste, which are perfectly fine and quite delectable. Serve immediately: The tahdig loses its crunch if it sits too long, so dig in right away.