Chop the smoked turkey or mushrooms into small pieces. In a large soup pot, sauté over medium heat for about 8 to 10 minutes until golden and slightly crispy. Remove and set aside.
In the same pot, add the chopped onion and sauté for about 5 minutes until soft and translucent.
Sprinkle in the flour and cook for 1 minute, stirring constantly. Slowly whisk in the milk until smooth.
Pour in the broth, add the diced potatoes and minced garlic, and stir well. Bring to a simmer, then reduce heat and cook gently for about 20 minutes.
Once the potatoes are tender, use a potato masher to mash part of them right in the pot.
Reduce heat to low. Stir in the sour cream, most of the cheddar, and the cooked turkey or mushrooms. Mix until the cheese melts.
Ladle into bowls and top with remaining cheddar, chopped scallions, and a few crispy turkey or mushroom bits. Serve hot and enjoy.
Notes
This soup can be made ahead of time for deeper flavors. Store in an airtight container for up to 4 days or freeze for up to 3 months. Reheat gently on low heat.