Preparation Working in batches, coarsely grate cabbage and beets in food processor fitted with grating blade. Set aside. Melt butter in heavy large skillet over medium heat. Add onions and sauté until brown, about 15 minutes. Mix in cabbage and beets. Add 1/2 cup water and vinegar. Cover; simmer until vegetables are tender, stirring occasionally and adding water by tablespoonfuls if mixture is dry, about 30 minutes. Season with salt and pepper. Transfer to bowl; top with parsley.
Preparation Working in batches, coarsely grate cabbage and beets in food processor fitted with grating blade. Set aside. Melt butter in heavy large skillet over medium heat. Add onions and sauté until brown, about 15 minutes. Mix in cabbage and beets. Add 1/2 cup water and vinegar. Cover; simmer until vegetables are tender, stirring occasionally and adding water by tablespoonfuls if mixture is dry, about 30 minutes. Season with salt and pepper. Transfer to bowl; top with parsley.