Sauté the onions in 2 Tbs. butter. Salt lightly.
A few minutes later add mushrooms, 1 tsp. dill, ½ cup stock or water, tamari and paprika. Cover and simmer 15 minutes.
Melt remaining butter in a large saucepan. Whisk in flour, and cook, whisking, a few minutes.
Add milk. Cook, stirring frequently, over low heat about 10 minutes - until thick.
Stir in mushroom mixture and remaining stock.
Cover and simmer 10-15 minutes.
Just before serving add salt, pepper, lemon juice, sour cream and, if desired, extra dill.
Serve garnished with parsley.