I have regularly prepared this dish for over a quarter of a century. I want so much to say that it is mine; but, alas, I cannot. The recipe came from an International Vegetarian Cookbook. We do a "no-no" and add ground sirloin to it.
Remove stem and root ends from onion; cut in half lengthwise and thinly slice onion lengthwise so that it falls into slivers.
Add butter in a deep, wide frying pan over medium heat. Add onion and garlic, and cook, stirring often, until onion begins to soften. Mix in paprika and nutmeg and cook, stirring, until onion is soft but not browned. Stir in mushrooms and cook, stirring occasionally, until liquid evaporates and mushrooms are lightly browned (10 to 15 minutes).
Add stock and bring to a boil over high heat. Reduce heat to medium and continue boiling gently until liquid is reduced by about a third (5 to 8 more minutes). Mix in spinach and stir just until wilted. Blend in sour cream, Worcestershire, and hot pepper seasoning. Season to taste with salt. Cook, stirring, just until heated through - do not boil. Serve over brown rice or pasta of your choice.