In a
Dutch oven, melt 3 tablespoons of butter and stir in the flour, constantly whisking for several minutes until the mixture is a rich, caramelized brown. Add the milk, broth, bouillon cube, and soy sauce, still whisking until the mixture is smooth. Add the mushroom mixture. Bring to a boil, reduce heat to medium, cover and simmer for 15 minutes, stirring occasionally. If the sauce is too thin, allow it to simmer uncovered for a few more minutes to reach desired consistency. If it's too thick, add a little extra milk. Stir in the sour cream and dill and simmer for another 2 minutes. Add salt and pepper to taste.