Heat oil in a deep fryer or deep pan to 325°F (165°C).
In a bowl, whisk flour, baking powder, baking soda, salt, pepper, garlic powder.
In another bowl, whisk buttermilk, egg, and hot sauce.
Dredge chicken in flour mix → dip in egg mix → dredge again in flour, press to coat well.
Fry chicken 3–5 mins per side until golden brown and cooked through (165°F inside).
Set on paper towels or rack to drain; repeat with remaining chicken.
For gravy: retain ¼ cup oil in pan, whisk in ¼ cup flour, cook 1 minute.
Slowly add 2–2½ cups milk, whisk until thickened (5–6 mins).
Season gravy with salt and pepper to taste.
Pour gravy over hot fried chicken and serve immediately.