Clean the fish from heads, entrails, and spiny fins; if you are using large fish, you also need to remove the bones.

Cut the onion into half rings, finely chop the garlic.

Pour olive oil into the bottom of a thick-walled pan, add onion, garlic, and fish, and simmer over medium heat for 10-15 minutes. If large bones, gill covers, or ridges remain on the fish, remove them.

Add diced potatoes and celery, salt, and water to cover the contents by about one finger, a bay leaf, and cook for at least half an hour under a closed lid over medium heat until the potatoes become completely soft.

While the soup is cooking, quickly fry the cherry tomatoes and finely chopped fennel in a frying pan with a bit of oil, but not completely cooked (al dente).

Then, remove the soup pot from the heat, remove the bay leaf, inspect the contents again for bones, fins, and heads, and puree everything in a blender until smooth.

Return to the stove, add a little water if the puree is too thick, and add the fried cherry tomatoes, fennel, and spices.

Simmer for about 10 minutes.

Balance the flavors to your liking with salt, lemon juice, and pepperoncini.

Serve immediately with a drizzle of olive oil and chopped fresh basil leaves.

If you have any stale bread, break it into pieces, put it on a plate, and pour the hot soup over it. It will be thicker and tastier.