How to Make It
In a small saucepan, combine the oil with the achiote and bring to a simmer. Transfer to a bowl and let stand until the achiote settles to the bottom.
Carefully pour the oil into a medium skillet, leaving the achiote behind. Add the onion and cook over moderate heat until softened and lightly browned. Add the pepper and cumin and stir for 30 seconds until fragrant. Add the peanuts, milk and cilantro and bring to a boil. Transfer the peanut sauce to a food processor and pulse until chunky. Season with salt and serve warm.