Marinate the Chicken: In a bowl, combine garam masala, garlic, ginger, and the chicken pieces. Mix well and let marinate for about 30 minutes.
Prepare the Tomatoes: Place the tomatoes in a bowl and cover with boiling water to soften. Set aside.
Sauté the Onions: Heat butter and oil in a large frying pan over medium-high heat. Add the onions and sauté for about 8 minutes until well browned. Reduce the heat if needed, properly browning the onions enhances the flavour of the dish.
Cook the Chicken: Add the marinated chicken to the pan and cook for about 10 minutes, stirring occasionally.
Add Tomatoes & Buttermilk: Drain the softened tomatoes and squeeze out the juices directly into the pan. Add the tomato pulp, chutney, or peach slices and buttermilk.
Simmer: Reduce heat to medium-low, cover, and let simmer until the chicken is tender and fully cooked.
Season & Serve: Add salt to taste and, if using, stir in the chopped chilies for extra heat. Serve warm with rice, naan, or extra chutney on the side.