In a small saucepan, bring the chicken stock and tomato purée to a boil.
In a blender, or with the side of a large knife on a cutting board, make a paste of the garlic and salt, adding a little stock if using the blender. Whisk the paste into the stock. Lower the heat and simmer, covered, for 10 minutes. Coarsely chop half of the basil. Stir into the soup and continue simmering for 5 mi