Preheat oven to 400. Prick washed potatoes & bake until a fork pierces to the center easily. Remove potatoes from oven & allow to fully cool. Remove skin & cut potatoes into 1/2" cubes. Set aside.
Melt butter in a large saucepan. Add onions & saute over low heat for 10 minutes or until onions are translucent. Add flour to onions & butter and cook 4 - 5 minutes, stirring well until flour is absorbed.
In a separate container, combine water, chicken base, yogurt & seasonings. Stir or whisk thoroughly to eliminate lumps. Add slowly to onion mixture, stirring constantly so no lumps form. Increase to medium heat & continue cooking until the soup begins to gently simmer.
Add milk & cream, stirring until smooth & lightly thickened. Simmer for 15 minutes - do not boil. Soup should just simmer lightly.
Add cubed baked potatoes & Stir to combine. Remove from heat & serve.
Top each serving with grated Cheddar cheese, sliced scallions & bacon pieces.