Heat the oven to 200C / 180C fan.

Halve the tomatoes and spread cut-side up on a tray with the quartered onion and unpeeled garlic. Drizzle with oil and season.

Roast 40-45 minutes until the edges are blackened in places. Those charred bits are flavour — do not pull them early.

Squeeze the garlic out of its skins and tip everything, including every scrap of tray juice, into a pot with the broth.

Simmer 5 minutes, then blend with the basil until smooth.

Finish with balsamic vinegar. It lifts the whole thing and stops it tasting flat.