To Prep
Combine marinade ingredients in a bowl. Add chicken and marinate in the fridge overnight.
To Cook
Boil potatoes until soft. Meanwhile, place cream and butter in a separate pot, bring to boil. Mash potatoes, add cream mixture. Stir in wasabi and salt to taste. Keep warm.
Preheat grill to medium. Grill chicken, skin side down, until browned. Increase heat to high, turn chicken and cook skin side up until meat is cooked through and skin is crisp.
Serve mash and chicken with extra wasabi.