Creating Rich Butter Chicken Biryani can be straightforward if you follow these simple steps:

1. Soak the Rice: Rinse the basmati rice under cold water and soak it in water for at least 30 minutes. Drain before cooking.
2. Prepare the Chicken Marinade: In a bowl, combine chicken pieces with ginger-garlic paste, yogurt, red chili powder, turmeric powder, and salt. Let it marinate for at least 30 minutes.
3. Cook the Onions: Heat oil and 1 tablespoon of butter in a large pot over medium heat. Add the sliced onions and sauté until golden brown.
4. Add Chicken: Once the onions are golden, add the marinated chicken. Cook until the chicken is browned and cooked through.
5. Make the Sauce: Stir in the tomato puree and cook for 5-7 minutes until the oil starts to separate from the mixture. Add garam masala, and mix well.
6. Add Cream: Lower the heat and stir in the heavy cream. Cook for another 5-10 minutes, allowing the flavors to meld. Adjust salt to taste.
7. Cook the Rice: In another pot, bring 4 cups of water to a boil, add salt, and then add the soaked basmati rice. Cook until the rice is 70% done. Drain and set aside.
8. Layer the Biryani: In the pot with the chicken, add the partially cooked rice on top. Dot the remaining butter on the rice, and sprinkle with chopped mint, cilantro, and slit green chilies.
9. Dum Cooking: Cover the pot with a tight lid and cook on low heat for about 20 minutes, allowing the flavors to infuse.
10. Fluff and Serve: Gently fluff the biryani with a fork before serving to mix the layers without breaking the rice.