Heat oil in a large heavy pot, over medium high heat.
Season the chicken with salt and pepper and cook until golden brown, about 2 minutes per side. Remove chicken from pot and reserve.
Add the potatoes to the same pot and cook until brown, about 5 minutes, stirring occasionally. Remove from pot and reserve.
Add more oil if necessary and add the red onions. Cook the onions for a few minutes, until they begin to brown, and reserve. I do not like to cook the onions too long, or they will lose its beautiful purple color.
Lower the heat to medium and stir fry the Massaman curry paste with the coconut milk for about 5 minutes, whisking to combine.
Add the broth, the chicken, the potatoes and the onions and bring it to a boil. Reduce heat, cover and cook until the chicken is tender and the potatoes are cooked, about 15-20 minutes.
Taste for seasoning and adjust salt and pepper to taste.
Stir in the peanuts and sprinkle the chopped cilantro.
Serve over rice!