Preheat oven to 400 and bake the potatoes for an hour or until done.
When the potatoes have cooked remove them from the oven to cool. As the potatoes cool, prepare soup by melting butter in a saucepan, and saute onion until light brown. Add flour to the onions to make a roux (similar to a thick paste).
Transfer to a large pot. Add stock, water, cornstarch, mashed potatoes, and spices to the pot and bring to a boil. Reduce heat and simmer for five minutes.
Cut potatoes in half lengthwise and scoop out the contents with a large spoon (or just peel the potatoes). Discard skin. Chop baked potato with a large knife to make chunks that are about 1/2 in. in size. The smaller the better. Add chopped baked potato and half-and-half to the pot. Bring soup back to a boil. Reduce heat and simmer the soup for another 15 minutes or until it has thickened.
Spoon about 1 1/2 c. soup into a bowl and top with about a tbsp. of shredded cheddar cheese, a half tsp. of crumbled bacon and a tsp. or so of chopped green onion (if desired). Repeat for remaining servings.
[My 2 Cents]
Bake the potatoes in a day in advance and refrigerate until needed in the recipe. This not only could save time, but also makes it easier to peel the potatoes cold and firm when they have been chilled. This cuts the prep time nearly in half when it comes to preparing the soup the day of. For a change, serve soup in a bread bowl. It makes for a fun, quick way to enjoy soup and bread at the same time.
Adapted from Top Secret Recipes