Add ¼ cup unsalted butter and ½ cup diced onion to a large pot. Cook over medium heat until the onions are softened, then add 1 teaspoon minced garlic and cook for 1 minute.
Add 3 cups chopped cabbage and cook until it softens and wilts.
Add 3 large peeled and chopped russet potatoes,6 cups vegetable broth,1 teaspoon salt, and ¼ teaspoon black pepper. Bring to a simmer and cook for 20 minutes or until the potatoes are tender.
Use an immersion blender to mostly blend the soup but still leave some potato chunks for added texture. The soup will be thick. You may use a food processor instead.
Stir in 1 cup half and half and 2 cups chopped kale leaves. Heat the soup until the kale slightly wilts. Serve the soup with sliced green onion and chopped cooked bacon for garnish.