Melt the butter and saute your onions directly in your soup pot over medium heat. You want the onions to go translucent, about ten minutes.
Add the mushrooms and stir, cooking until they start to release some of their moisture and shrink, about another 5-10 minutes.
Mix the flour and paprika into the mushrooms and onions, cooking further for 2-3 minutes.
Add in the stock, soy sauce, and milk. Stir and bring to a boil, then reduce the heat to a simmer for another 10 or so minutes.
When ready to eat, remove from the heat. Mix in the sour cream, lemon, dill, and parsley. Add additional dill and sour cream individually to taste, along with salt and pepper if you like.