Cook 6 Savoy cabbage leaves in boiling water, about 2 minutes. Rinse under cold water and pat dry; slice in half. Mix 1/4 cup each mayonnaise and chopped parsley and/or dill; spread on the cabbage leaves. Cut 2 slices rye bread into strips. Slice 1/2 pound corned beef into strips and toss with a spoonful of whole-grain mustard. Top the cabbage leaves with a few strips each of the bread and corned beef. Roll up and slice in half.