Cook bacon until crisp in a large soup pot. Remove bacon strips with a slotted spoon and set aside. Lightly saute potatoes, onion, and garlic in bacon drippings. Add stock, kale, salt, and pepper and simmer for an hour or until potatoes are soft. Mix soup in batches in blender until it is smooth. Return to pot and thin with stock or milk if necessary. Crumble bacon and sprinkle over soup as garnish.