Step 1. Place a rack in middle of oven and preheat to 425°. Combine ½ tsp. saffron (15–20 threads) and 1 Tbsp. warm water in a large bowl; set aside.. Step 2. Meanwhile, place about ½ cup thinly sliced medium onion in a medium bowl of ice water and set aside to soak. Finely chop 1¼ cups (lightly packed) mixed tender herb leaves with tender stems (such as parsley, dill, cilantro, and/or mint) and set aside.. Step 3. Heat 5 Tbsp. extra-virgin olive oil in a large skillet over medium. Add 2 tsp. ground coriander, 2 tsp. ground cumin, 2 tsp. vegetable or chicken bouillon paste, ½ tsp. freshly ground pepper, ¼ tsp. Diamond Crystal or Morton kosher salt, and remaining onions and cook, stirring often, until onions are deep brown and crisp in spots, 13–17 minutes.. Step 4. Add one 15-oz. can chickpeas, rinsed, to pan; increase heat to medium-high. Cook, stirring occasionally, until slightly crisped, 6–8 minutes. Remove from heat; mix in ½ cup dried tart cherries or unsweetened dried cranberries and reserved chopped herbs. Season with more salt and pepper if needed.. Step 5. Cook 2 cups basmati rice, rinsed, in a medium saucepan of boiling generously salted water until just al dente, about 5 minutes, then drain.. Step 6. Add 2 large egg yolks, ¼ cup mayonnaise, ¾ cup whole-milk Greek yogurt, and ¼ tsp. Diamond Crystal or Morton kosher salt to reserved bowl with saffron; whisk until smooth. Fold in rice.. Step 7. Pour 3 Tbsp. extra-virgin olive oil into an 8×8″ glass baking dish and spread around to coat bottom and sides. Add 2 cups rice mixture and press with a flat-bottomed measuring cup or a spatula to compress. Mound onion mixture over, leaving a ½” border on all sides, and flatten slightly. Spoon remaining rice mixture on top and lightly press down to compress. Cover baking dish with foil.. Step 8. Bake tachin until bottom and sides are deep golden, 55–65 minutes. Let cool 10 minutes, then remove foil and run a paring knife around sides to loosen. Place a platter or large plate upside down over baking dish and hold together as you quickly turn over; remove baking dish.. Step 9. Whisk remaining ½ cup whole-milk Greek yogurt and 2 Tbsp. water in a small bowl (it should be thin enough to drizzle; add more water if needed). Season with salt and pepper.. Step 10. Drain reserved onion. Toss onion, a pinch of kosher salt, remaining 1¼ cups (lightly packed) mixed tender herb leaves with tender stems, and remaining 1 Tbsp. extra-virgin olive oil in same bowl to combine. Mound salad on top of tachin; serve with yogurt sauce.
