In a large Dutch, combine potatoes, onion, chicken stock and pepper. Bring to a boil. Reduce heat, cover, and simmer until vegetables are tender, about 25 to 30 minutes.
Blend or process cooked potato mixture, a little at a time, until smooth. Return to the pot and add butter and chopped spinach. Cook, uncovered, over low heat for about 3 to 5 minutes, until spinach is wilted. Stir in sausages; serve immediately. Serving size is about 1 cup.