In a heavy-bottomed pot, add the vegetables and fill with water until it covers them.
When it starts to foam, add the onions and thyme and cook over medium-low heat until tender, about 10 minutes. For a smooth soup, use a blender and purée until smooth
About 30minutes later, add the cube of bouquet Garni and continue cooking over medium-low heat until tender, about 15-20 minutes later.
Then use a blender and purée until smooth.
You may add some creme fraiche for creaminess, it changes the taste a little too.
All for the better, not the worst.
You may add some pine nuts for a crunch or croutons.
To ensure a smooth soup pass it through a chinois or a conical sieve.