How to cook
Start with the croutons, grate the garlic clove and mix with the fat of your choice. Remove the crust from the bread slices, cut the soft part into cubes, and place in a small tray.
Drizzle the bread cubes with the garlicky fat and mix well. Place the tray in a preheated oven at 356°F (180 degrees) and bake, periodically stirring the croutons until light brown.
Peel and chop onions, carrots, celery root, potatoes, and mushrooms in larger pieces. Put them in salted water over medium heat to boil until soft.
Strain the broth from the soup, puree the cooked vegetables, adding parts of the broth while blending. Dilute the sour cream with the milk and add it to the soup.
Add the vegetable seasoning, salt to taste, sprinkle with black pepper to taste, and butter. Bring the soup to a boil and remove from the heat. Serve with croutons.