Melt Butter in a large skillet.Add Onion, Minced Garlic and Mushrooms.Saute for a few minutes on Medium Heat.Add Spinach, sprinkle with salt and black pepper; saute until wilted.Add mixture to a Slow Cooker.Add all remaining ingredients to Slow Cooker.Lightly Stir.Cook on High for 4 hours.Note: For a creamier consistency, whisk â…“ C. of flour in 1 C. of milk and add to soup during last 30 minutes of cooking time.