Peel the zucchini with a potato peeler. Set the peel aside and cube the zucchini. Chop the onion and the garlic cloves very finely.
Melt 1 tablespoon butter in a soup pot. Add the onion and cook gently until translucent. Add the garlic, stir shortly, then add the chopped zucchini. Cook for about 4-5 minutes, until the zucchini cubes turn golden.
Separate the egg yolk from the egg white. Set the egg yolk aside for later and beat the egg white with a pinch of salt until stiff. Gently fold the stiff egg white in the zucchini-cheese mixture. Spread the mixture on top of the roasted baguette slices, place the slices on a baking tray and bake the baguettes for about 10 minutes until the soufflés are nicely puffed.
Preheat the oven to 220 degrees Celsius/ 430 degrees Fahrenheit.
In the meanwhile finish the soup. Purée the soup. Whisk a ladle of the soup with the egg yolk until smooth. Give this mixture in a slow stream to the soup while whisking all the time. Adjust the taste with salt and pepper.
Pour the soup into the bowl and place one piece of the baguette on top. Serve immediately, you will not want your baguette to become soggy.