The round heads, in green, red (more like purple), and savoy (which has green, crinkly veined leaves), should feel tight and heavy for their size. Discard the two or three outer leaves and rinse the head in cold water before using. Cut the head into quarters through the stem end, then cut the core out of each piece. On a cutting board, place a wedge cut side down. With a sharp chef’s knife, cut the cabbage crosswise into thin (or thick) slices.