Cook the diced sausage and onion in a large pan over medium-high heat until the onion is softened and the sausage begins to brown, 6 to 8 minutes.
Add the sausage and onion mix to the slow cooker along with the diced potatoes and chicken broth.
Cover and cook on low for 4 to 5 hours or until potatoes are tender.
Stir in the heavy cream, cheddar cheese, and cayenne, stir until cheese is melted.
Combine the cornstarch and water together in a small bowl and slowly stir into the soup, continue to stir until thickened. Add salt & pepper to taste.
