Heat the 60 ml olive oil in a 28 cm / 11-inch Dutch oven (5-quart / 4.7 L) over medium-low heat. Add the onion, carrot, celery and parsley stems, and cook for 10 minutes, stirring often, until soft and pale without browning. Add the 3 smashed garlic cloves and cook for 1 minute until fragrant.

Pour in the wine and boil for 2 minutes. Stir in the passata, water, bay leaf, salt and pepper, then add the fish. Bring to a gentle simmer and cook for 25 minutes, skimming any foam, until the fish falls apart when pressed with a spoon.

While the soup simmers, heat the oven to 200 C / 400 F. Arrange the 12 bread slices on a 33 x 46 cm / 13 x 18 inch sheet pan and bake for 8 to 10 minutes, flipping once, until dry and golden. Rub each hot slice with the cut garlic clove and brush with a little of the 2 tbsp olive oil.

Remove the bay leaf and blend the soup with an immersion blender, or in batches in a countertop blender, for 2 full minutes until smooth. Press it through a 20 cm / 8-inch fine-mesh sieve into a clean pot, pushing with the back of a ladle until only dry bone and skin remain, and discard them. The soup should pour like thin cream, so add hot water 50 ml at a time if it's thick.

Warm the strained soup over low heat for 2 to 3 minutes until steaming, then taste and add salt if needed. Put 2 toast slices in each wide bowl, ladle the soup over, and finish with a drizzle of olive oil and the parsley leaves. Serve right away, while the toast still holds its shape.