Step 1: Melt the unsalted butter in a large pot over medium heat. Add the diced yellow onion and sauté for about 5 minutes until translucent and soft.
Step 2: Add the sliced cremini mushrooms and sauté for another 7-10 minutes until golden brown.
Step 3: Pour in the vegetable stock and soy sauce. Stir in the paprika, dill, and thyme. Bring to a simmer and cook for about 5 minutes.
Step 4: In a small bowl, whisk together the whole milk and flour until smooth. Gradually add this mixture into the pot, stirring constantly. Simmer for about 5 minutes until thickened.
Step 5: Remove from heat and stir in the sour cream and lemon juice. Adjust seasoning if needed.
Step 6: Ladle the soup into bowls and sprinkle fresh chopped parsley on top. Serve warm.
Notes
For a bit of heat, add red pepper flakes or hot sauce. This soup can be made ahead of time and tastes even better the next day.