Cut the chicken breasts into thin strips. Cut the spring onions into rings. Peel the potatoes and cut into 1 cm cubes. Peel the fresh ginger and finely chop it. Cut the lemongrass stalk into three pieces.
Chop the fresh coriander, separating the stems and roots from the leaves.
Heat oil in a wok over medium-high heat. Fry the chicken strips for 2-3 minutes until they are no longer pink. Add the potato cubes and fry for 2 minutes. Deglaze with the coconut milk. Add the curry paste, peanut butter, sugar, vinegar, fish sauce, peanuts, ginger, lemongrass pieces, and coriander stems and roots. Reduce heat to medium and simmer for approximately 40 minutes, stirring every 2-3 minutes. If too much liquid evaporates, add water as needed. The chicken should reach an internal temperature of 74°C (165°F).
Remove the lemongrass pieces from the curry. Stir in the spring onions and simmer over medium heat for 5 minutes. Add the coriander leaves and serve.