Blend the garlic, onions, lemongrass, turmeric root, galangal, small red chilies, and large red chilies with a little water.
Add coconut milk, salt, fish sauce, and sugar to the blended mixture in a pot. Add halved chicken and simmer for 30 minutes until the chicken is cooked and the sauce has thickened slightly.
Air fry the chicken at 150°C for 15 minutes.
Brush the chicken with additional spicy sauce and air fry again at 170°C for 5 minutes to achieve a crispy texture.
Prepare the remaining spicy sauce by boiling it in a separate pot. Add tamarind paste, lemongrass (slashed), and fennel seeds, allowing it to thicken quickly.
Serve the chicken with the thickened spicy sauce poured over it.