For the beer soup with grilled bread slices, halve the onions and cut them into thin slices. Heat the olive oil and fry the onion strips with the sugar until light brown.
Pour in the vegetable soup and the beer and add the spices, except for the parsley and the vinegar. Bring the soup to a boil and simmer for 10 minutes.
Thinly sprinkle the bread slices with the parmesan and grill under supervision at 200°C until golden brown. Season the soup with vinegar and salt.
Serve the beer soup with the grilled bread slices and the parsley.