Brush the saffron milk caps (10½ oz/300 g) clean with a dry brush, and rinse only the stickiest ones. Chop them into small pieces. Dice one large onion and crush the garlic (4 cloves).
Scoop the seeds out of the red kuri squash (about 3 lb/1.4 kg) and cut it into small cubes. Kuri can keep its skin, but peel other types of squash if needed.
Warm the olive oil (2 tbsp/30 ml) in a medium pot and cook the onion until it’s soft and lightly golden.
Add the squash, then pour in the water or stock (4 cups/950 ml). Add the salt (3 tsp/18 g in total, saving a pinch for the mushrooms), the marjoram (1 tsp/1 g) and the bay leaf. Bring to a boil, cover, and simmer over medium heat for around 20 minutes, until the cubes are fork-tender.
Meanwhile, heat the olive oil (2 tbsp/30 ml) in a large saucepan. Fry the mushrooms with the garlic, the pinch of salt and the black pepper (2 tsp/5 g) for about 10 minutes, until their liquid evaporates.
Cube the dry bread (2 small pieces) and fry it in the olive oil (2 tbsp/30 ml) in a separate pan until crisp and golden.
Remove the bay leaf and purée the soup with a hand blender. Stir in the mushrooms, setting a handful aside.
Ladle the soup into bowls and swirl in the sour cream (6 tbsp/90 g in total). Top with the croutons, the reserved mushrooms and chopped parsley. Enjoy!