Start by baking potatoes for about an hour in a preheated oven (400 F). Then, set them aside to cool for a few minutes.
Melt butter in a saucepan and add onions to it. Saute the onions until brown in color. Stir in flour and mix to make roux for the soup.
Pour in water along with stock, mashed potatoes, and spices. Bring the mixture to a boil and reduce the heat. Let it simmer for about 5 minutes.
Stir in chopped baked potatoes and heavy cream. Bring it to a boil, reduce the heat, and let it simmer again for about 15 minutes until the soup is thick.
Now, transfer soup into a bowl with cheddar cheese on top. Garnish with a half teaspoon of bacon and chopped green onion and serve.