Clean the broccoli, cut off the roses, peel the stems if necessary.
First of all, cook the roses in salted water until al dente, remove them with a skimmer and rinse with ice cold water. In the same water, soften the stalks and add the onion, roughly chopped, and the garlic.
The vegetables should now be soft enough to pass through a sieve, but it is easier to finely grind them in a hand blender, adding as much cooking water as necessary to achieve the right soup consistency.
Finally, blend in the ice-cold butter to make the soup creamy.
Season with cayenne, salt, pepper, soy sauce and a few drops of lemon juice. Heat the broccoli florets in this soup one more time and bring to the table in soup cups or soup plates.
Let the cauliflower florets swim in it. Of course, the whole soup can be made with cauliflower as well.