Serves: Six 240ml servings1) Heat the olive oil in a soup pot over medium heat. Add the onion, garlic, sage, 5g salt and season with pepper, to taste. Cook, covered, stirring occasionally, until soft and fragrant, about 15 mins.
2) Raise heat to medium-high, add the tomatoes, and cook, stirring with a wooden spoon, until the tomatoes break up and the onions brown slightly, about 7 mins.
3) Add the squash and the remaining 5g salt, and continue to cook, stirring occasionally, until the squash is tender, about 12 mins. Add the broth, bring to a simmer, and cook, uncovered, until the vegetables tender, about 20 mins. Set aside to cool slightly.
4) Working in batches, puree the soup in a blender, or with an immersion blender. Return the soup to the pot and reheat over medium heat. Stir in the vinegar. Serve the soup in warm bowls with a touch of Parmesan cheese if desired.