Rub chicken with salt and pepper. Heat oil in a frypan then brown meat on both sides. Reduce temperature and keep cooking until meat is no longer pink. Remove from frypan and keep warm.
Increase temperature to medium and add sugar to the frypan. Caramelise sugar while stirring constantly.
Stir in butter and cassis until melted then add rhubarb. Cook in the sauce until it is soft but doesn't fall apart. Season with salt and pepper.
Layer the rhubarb onto chicken and drizzle with the sauce.