Cut cabbage in half lengthwise and cut out core. Cut each half lengthwise again, then cut each quarter crosswise into 1/2 inch cubes.
Melt butter in large saucepan over medium heat. Add the onion and cook, stirring occasionally, 10-15 minutes, or until soft. Add cabbage and saute, stirring occasionally, for 25 minutes, or until tender. Add the vinegar, sugar, and cumin and mix well. Lower heat to medium low and simmer 20 minutes more, until juices are syrupy. Cabbage should be tender but not mushy. Remove from heat and season with salt and pepper.