Cut cabbage in half lengthwise and cut out the core. Cut each half in half again lengthwise. Then cut each quarter crosswise into ¾ to ½ inch cubes.
Melt butter in a large saucepan over medium heat. Add the onion and cook, stirring occasionally, until soft and golden brown (10 to 15 minutes). Add the cabbage and sauté, stirring occasionally, until tender (25 minutes). Add vinegar, sugar, and cumin. Mix well, lower to medium-low heat, and simmer for 20 minutes until juices are syrupy and the cabbage appears shiny (should be tender but not mushy). Remove from heat and season with salt and pepper.