Pour 2 tablespoons of olive oil into a large saucepan over medium heat. Allow it to warm up but not smoke.

Add the chopped white mushrooms and cook, stirring occasionally, until their water has fully evaporated.

Add the chopped leek and continue to cook until softened and slightly golden. Stir frequently to prevent burning.

Stir in the chopped garlic and pour in the beef stock. Mix well to deglaze the pan and infuse the flavors.

Cover the saucepan with a lid and let the soup simmer gently for 15 minutes to develop the flavors.

Add the thyme sprigs and a pinch of freshly grated nutmeg for warmth and aroma.

Remove the saucepan from the heat. Use an immersion blender or transfer the soup to a blender. Blend until completely smooth and velvety.

Stir in the crème fraîche for a rich, creamy texture. If the soup needs extra thickness, dissolve cornstarch in water and whisk it into the soup while reheating slightly until thickened.

Ladle the soup into bowls and garnish with sautéed mushroom slices for extra elegance.

Sprinkle with freshly ground black pepper for a final touch of flavor.