Melt butter over medium to medium low heat in a large dutch oven with a lid; add onion and saute until softened (about 8-10 minutes). Remove core and shred cabbage (about ⅛-inch thick shreds, or to preference). Peel optional beet, remove top and tail, shred. Add cabbage, beet and all remaining ingredients to dutch oven. Cover and cook over low heat for about 45 minutes or until tender.