Scrub potatoes in several places and bake for 1 hour or until tender in the preheated oven at 400 degrees. Peel the potatoes when cool down completely.
Melt butter in a pot over medium-low heat, add onion and garlic and cook until soft but not brown. Add 3 tablespoons all-purpose flour and cook for 1 minute.
Now, add 2/3 of the potatoes and mash with the help of a potato masher. Add milk, broth, salt, and pepper and mix well. Let the soup simmer and keep the consistency you want, stirring occasionally.
Taste the soup before serving and add a little more salt and pepper if needed.
Cut the remaining potatoes into cubes, add to the soup and stir gently.
Pour the soup into a serving bowl, garnish with toppings and serve.