Preheat oven to 400 degrees and bake the potatoes or 1 hour or until done. When potatoes have cooked remove them from the oven to cool. As potatoes cool prepare soup by melting butter in a large saucepan, and saute; onion until light brown. Add the flour to the onions and stir to make a roux. Add stock, water, cornstarch, mashed potatoes, and spices to the pot and bring to a boil.
Reduce heat and simmer for 5 minutes. Cut potatoes in half lengthwise and scoop out contents with a large spoon. Discard skin. Chop baked potato with a large knife to make chunks that are about 1/2-inch in size. Add chopped baked potato and half-and-half to the saucepan, bring soup back to a boil, then reduce heat and simmer the soup for another 15 minutes or until it is thick.
Spoon about 1 1/2 cups of soup into a bowl and top with about a tablespoon of shredded cheddar cheese, a half tablespoon of crumbled bacon and a teaspoon or so of chopped green onion. Repeat for remaining servings.