Cut chicken into 1 ½-inch (3.5 cm) pieces and place in large bowl. In another bowl, whisk together buttermilk, sugar and half each of the garam masala, salt, coriander, turmeric, garlic powder, pepper and ginger.
Whisk in cayenne and pour over chicken pieces. Cover and refrigerate for at least 8 hours or up to overnight.
Spicy Peach Yogurt Dip: In a small pot, combine peaches, chili sauce, water and ginger and bring to a simmer over medium heat and cook for about 15 minutes or until thickened and peaches are very soft. Let cool slightly and transfer to a blender with yogurt and sriracha; blend until smooth. Transfer to a jar and cover and refrigerate until cold.
In a large, shallow dish, whisk together flour, cornstarch, paprika and remaining garam masala, salt, coriander, turmeric, garlic powder pepper and ginger. Dredge chicken, one piece at a time, in flour mixture, coating well, and then place on large baking sheet.
Meanwhile, in a large, heavy, high-sided pot, heat oil over medium heat to 350°F (180°C). Add chicken in batches to oil and fry for about 3 minutes or until golden brown and no longer pink inside. Using tongs, transfer chicken pieces to a rack set over baking sheet. Repeat with remaining chicken.
Serve chicken with spicy peach yogurt dip.