Preheat oven to 400 degrees and bake the potatoes for 1 hour. Once done, take them out to cool.
In a pot melt the butter
Add onions and sauté till they brown
Add the flour to the melted butter and onions to make a roux
Now add the chicken stock
Dissolve the cornstarch in the water and add it to the pot
Now add the mashed potatoes and all the spices
Stir and bring to a boil. Then reduce the heat and let simmer for about 5 minutes.
In the meantime, peel the baked potatoes, cut them into chunks and add them to the simmering pot.
Add the half-and-half and bring again to boil
Once boiled, reduce heat and let it simmer till it thickens, about 15 mins
Serve the soup into bowls and garnish individually. Add a little helping of bacon, cheddar cheese and scallion into each bowl