While your chicken and potatoes are cooking. Peel and grate the garlic (or use a garlic press) then heat a frying pan on medium heat and add the butter. Once the butter has melted, add the cavolo nero, stir, add a splash of water, and the garlic and pop on a lid. Cook until the leaves are tender, 4-5 mins, stir every now and then. When ready, season with salt and pepper and keep to one side