Slow Cooker Cheesy Ham Chowder

Name: Slow Cooker Cheesy Ham Chowder
Ingredients: 1 1/2 lbs. russet potatoes, peeled and diced into 1/2 cubes ((about 3 medium sized potatoes)); 20 oz canned corn (drained), or frozen corn (thawed); 4 cups cubed ham steaks, diced into 1/2 cubes; 1 large yellow onion, diced; 4 ribs celery, diced; 4-5 cloves garlic, minced; 1/2 tsp black pepper; 4 cups chicken stock (or broth); 2 cups whole Milk; 2 Tbsp cornstarch; 2 cups shredded cheddar cheese; 1 cup sour cream; 2 Tbsp fresh minced parsley; extra parsley, pepper and cheese, (for garnish)