This recipe is inspired by Julia Child's mushroom soup in Mastering the Art of French Cooking Vol. 1. These mushrooms are sliced, not minced, so it has a robust texture. If you like a smoother consistency, blend it in a blender or with an immersion blender on high for several minutes.
In a large pot, melt 3 tablespoons butter.
Add the onions and cook them until they are soft and translucent.
Sprinkle 3 tablespoons flour over the onions and cook the flour for 2 minutes.
Whisk in 6 cups of chicken stock, bring to a boil, and immediately reduce to a simmer.
Add the parsley, bay leaf, thyme, chopped mushroom stems, salt, and pepper. Simmer for 20 minutes stirring occasionally.
Strain and return the soup to the pot. Discard the parsley, bay leaf, thyme, and mushroom stems.
In a separate pan, melt 2 tablespoons butter.
Add the sliced mushrooms to the melted butter with 1/4 teaspoon salt, and 1 teaspoon lemon juice.
Sauté the mushrooms until they are brown over medium-high heat, about 5 minutes.
Add the mushrooms and their juices into the soup and simmer for 10 minutes.**
Beat the egg yolks and cream together in a small bowl.
Take the soup off the heat and slowly whisk in the cream mixture.
Taste and correct seasoning with salt and fresh ground pepper if needed.
Ladle the soup into bowls and garnish with parsley.
**After you finish step 10, you can freeze the soup in an airtight container for up to 3-4 months. Once the yolks and cream are added, this soup will last refrigerated for 7 days.