Add diced potatoes, diced onion, minced garlic, thyme, parsley, butter, mustard powder, and chicken broth to the slow cooker. Season with salt and pepper.
Stir, then cover and cook for 6-8 hours on low or on high for 3-4 hours.
During the last 30 minutes of cooking, whisk cornstarch and cream together. Add sour cream. Stir into soup. Cook for 15-30 minutes or until thickened. Puree or mash part of the soup if you want a creamier texture. If needed add more cream or milk.
Stir in cheese until well melted. Taste and adjust for salt and pepper.
Serve topped with sour cream, more cheese, and cooked, crumbled bacon.