Take a medium mixing bowl and add the sour cream, mayonnaise, buttermilk, and lemon juice.
Whisk the mixture well until it becomes smooth and creamy.
Add Dijon mustard, garlic powder, dried thyme, dried dill weed, black pepper, and cayenne pepper.
Whisk again until all ingredients are fully combined.
Cover the bowl with plastic wrap or transfer the sauce to an airtight container.
Place it in the refrigerator for at least one hour to allow the flavors to blend.
Remove from the refrigerator, stir once, and serve with freshly fried mushrooms.
Notes
Chilling the sauce improves the overall taste.Always taste before serving and adjust seasoning if needed.If the sauce becomes too thick, add a small amount of buttermilk.Serve the sauce cold for the best contrast with hot fried mushrooms.