Cut the pummelo in half. Juice and zest one half. Peel the other half of the pummelo with a sharp knife, cutting away as much of the peel and bitter white pith as you can. Separate it into sections, cutting them in half if the pummelo is very large. If the juice does not make about 2/3 cup, you can add water or a little grapefruit juice to make up the rest.