Bake potatoes 1 hour or until tender when pierced. Peel when cool enough to handle.
Melt Butter in a 4 to 6 qt pot over medium low heat. Stir in onions and garlic, cover and cook 10 minutes until soft, but not brown.
Add 2/3 of the potatoes and mash with a potato masher. Add broth, milk, salt and pepper. Bring to a simmer, stirring occasionally. Cut remaining potatoes in small cubes. Add to soup and stir gently to reheat. Sprinkle each serving with toppings.