In a large bowl whisk together the seeded hot pepper, minced garlic, grated ginger, yogurt, Kashmiri chili powder, turmeric, garam masala, 1 tablespoon coarse salt, and lemon juice; taste and adjust seasoning.
Remove skin from the chicken pieces and make 2–3 shallow slashes (about 1/4–1/2 inch) on each piece.
Add the chicken to the marinade, toss to coat thoroughly, cover, and refrigerate for at least 4 hours or up to 24 hours.
Heat 1/2 cup avocado oil in a 10-quart Dutch oven over medium heat and fry the julienned red onions, stirring occasionally, until brown and crispy (about 15–18 minutes); drain on paper towels and set aside; leave any remaining oil in the pot.
Rinse the basmati rice in a fine-mesh strainer under cold water until the water runs clear, then soak briefly in cold water and set aside.
In a separate 6-quart pot, melt 2 tablespoons ghee over medium-high heat and sauté the bay leaf, star anise, cloves, green and black cardamom pods, cinnamon stick, cumin seeds, and fennel seeds for 1–2 minutes until fragrant.
Add about 1 gallon of water to the spice pot, bring to a boil, season with salt, then add the rinsed rice and cook 5–7 minutes until rice is about 75% cooked (al dente); drain and spread on a sheet tray to cool.
Return the pot with the frying oil to medium-high heat, add the marinated chicken and the sliced potatoes, and cook 5–6 minutes, stirring so potatoes are mixed with the chicken; flip the pieces and cook another 5–6 minutes.
Add two-thirds of the fried onions, 3 tablespoons minced mint, 3 tablespoons minced cilantro, and the diced tomatoes to the chicken-potato mixture; cook 3–4 minutes to combine flavors.
Flatten the chicken and potato layer, then evenly top with half the cooked rice, sprinkle 2 tablespoons minced mint, 2 tablespoons minced cilantro, half of the remaining fried onions, and salt; do not pack the rice.
Repeat the layering with the remaining rice, mint, cilantro, and fried onions; dot the top with the remaining ghee (about 4 tablespoons).
In a small bowl warm the milk and steep the saffron threads for 2–3 minutes until very yellow, then strain and drizzle the saffron milk in a circular motion over the rice.
Cover the pot tightly with foil and the lid and cook over low heat for 30–35 minutes, until the chicken is cooked through and the potatoes are tender.
Serve portions of chicken, potatoes, and rice, and garnish with any remaining fried onions, minced cilantro, and mint.