Heat a pan and add the oil and Massaman curry paste. Sauté until fragrant, then gradually add the coconut milk, stirring until the oil separates.

Add the chicken and stir-fry. Gradually pour in the coconut milk and water until the chicken is covered. Reduce the heat to low, cover, and simmer for about 30 minutes.

Season with fish sauce, salt, tamarind paste, and palm sugar. Taste and adjust the seasoning as desired.

Add the peanuts, potatoes, and onion. Simmer for another 10 minutes. Turn off the heat, transfer to a serving bowl, and serve.