Clean the pumpkin by removing the rind, seeds and filaments and cut it into cubes of one centimeter on each side.
Wash the potatoes, peel them and cut them into cubes as was done for the pumpkin.
Wash the celery and slice it about one centimeter thick. If the rib is small, that's fine, otherwise cut each slice into 2-3 parts in orderto obtain small pieces about the same size as pumpkin and potatoes.
Wash the chard and chop the leaves into small pieces. Wash the cauliflower florets and separate them to obtain small flowers.
Heat the vegetable broth.
In a soup pot put the oil, the peeled and finely chopped onion, and brown it on a low flame until it is transparent.
Add the vegetables and cook, stirring for a few minutes.
Add the vegetable broth, a generous pinch of coarse salt, mix and bring to the boil again.
Cook covered for 30 minutes over low heat.
Serve hot or lukewarm with croutons.