Preheat your oven to 375°F (190°C). Toss the brioche cubes with olive oil, salt, and pepper. Spread them on a baking sheet and bake for 10-12 minutes until golden and crispy. Set aside.

Cook the Leeks and Mushrooms

In a large pot, heat the olive oil over medium heat. Add the sliced leeks and sauté until soft, about 5 minutes. Add the minced garlic and cook for an additional minute.

Add the Mushrooms

Stir in the sliced mushrooms and cook until they are softened and have released their moisture, about 8-10 minutes.

Add Broth and Miso

Pour in the vegetable broth and bring to a simmer. Add the miso paste and thyme, stirring until the miso is dissolved. Simmer for another 10 minutes.

Blend the Soup

Using an immersion blender, blend the soup until smooth (or blend in batches in a regular blender). If you prefer a chunkier texture, blend only half of it.

Final Touches

Stir in the heavy cream and season with salt and black pepper to taste. Heat through for a few minutes.

Serve

Ladle the soup into bowls, top with crispy brioche croutons, grated Parmesan cheese, and enjoy!