The skin of young zucchini is thin and need not be removed for most purposes, but the dark green skin of older zucchini can be bitter and should be removed. One garnishing treatment calls for just some of the skin to be discarded: using a potato peeler, shave the vegetable thinly lengthways to produce very thin slices. Throw away the first slice and the last, which consist mostly of green skin, and drop the remaining, green-edged slices into a pan of boiling water. Drain and refresh them under the cold tap as soon as the water returns to the boil.