Heat a stockpot over medium-high heat. Add the butter, olive oil, leeks, carrots, onion and celery. Sauté until onions and leeks begin to soften (about 6-8 minutes).
Add the mushrooms, and garlic; continue to sauté about 3-4 minutes, stirring constantly, until mushrooms soften.
Turn up the heat to high and add the potatoes, turkey or chicken stock, bay leaf and seasonings. Bring to a boil and then reduce heat to maintain a gentle simmer. Continue to simmer until potatoes are “al dente.”
Turn off heat. In a blender or food processor, add the cup of milk, about 2 ladle-fulls of the soup and 1 ladle-full of the broth only. Blend until completely puréed.
Place puréed soup back in the pot. Add the shredded turkey (or chicken) to the soup. Stir to combine. Cover stockpot and allow soup to sit for 5 minutes to warm the chicken.
Then, remove the bay leaf and re-season to taste with salt and pepper, if necessary. Serve with grain-free brown bread rolls with a dollop of cranberry sauce. Mmm!!!