Irish Colcannon and Thyme Leaf Soup

This soup re-interprets Irish classics: colcannon, a dish of mashed potatoes and kale or white cabbage. Sprinkle with thyme and black pepper.
Melt 1 tablespoon butter in a large saucepan over medium-high heat. Add the potatoes, onion, 1/4 teaspoon salt and 1/4 teaspoon pepper. Cover and cook for 6 minutes. Add broth and 2 cups water; bring to a boil. Cook for 10 minutes or until the potatoes are tender.Combine 3 tablespoons of water and the remaining 1 tablespoon of butter in a large roasting pan; bring to a boil. Add the cabbage and thyme. Cover and cook for 5 minutes, stirring occasionally. Remove from heat; add remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper.Put half of the potato mixture in a blender. Remove the center part of the blender lid (to release steam); secure the blender lid to the blender. Cover the hole in the blender lid with a clean towel (to avoid splashing). Whisk until smooth. Pour into a large bowl. Repeat with the remaining potato mixture. Add the potato mixture to the cabbage mixture; cook over medium-low heat until completely warmed through.