This is one of my favorite soups and I like to make it with different kinds of mushrooms. I think my favorite is a mix of white and portabella.
4 tablespoons unsalted butter or 2 T olive oil
2 cups chopped onions
3-4 cloves minced garlic
1 pound fresh mushrooms, sliced
3 teaspoons dried dill weed
5-6 shakes cayenne pepper
2 tablespoon paprika
1 tablespoon soy sauce
2 cups chicken (or vegetable) broth
1 cup milk
5 tablespoons all-purpose flour (or 1-2 T corn starch or dry potato flakes for gluten-free)
1 teaspoon salt
ground black pepper to taste
2 teaspoons lemon juice
1/4 cup chopped fresh parsley
1/2 cup sour cream
Melt the butter in a large pot over medium heat. Saute onions. Add garlic and mushrooms and saute until softened. Stir in dill, paprika, cayanne, soy sauce and broth. Reduce heat to low, cover, and simmer for 15 minutes.
In a separate small bowl, whisk milk and flour together. Pour into soup and stir well to blend. Cover and simmer for 15 more minutes, stirring occasionally.
Finally, stir in the salt and pepper, lemon juice, parsley and sour cream. Mix together and allow to heat through over low heat, about 3 to 5 minutes. Do not boil. Serve immediately.
Of course it tastes better if you let it sit for a day or overnight. I sometimes make it up to the point of adding the sour cream and stuff and refrigerate it overnight. The warm it up and add the sour cream et al.