Position a rack in the center of the oven and heat the oven to 350°F. Spread the bread cubes on a rimmed baking sheet and toast in the oven until lightly golden and crisp, about 15 minutes.
Bring a medium pot of well-salted water to a boil over high heat. Add the basil and cook until wilted, about 30 seconds. Drain and run under cold water. Pat dry with paper towels and roughly chop.
In a blender, purée the basil, tomatoes, garlic, and 2 cups ice-cold water for about 45 seconds. Strain through a fine sieve to remove the solids and return the purée to the blender.
Add the bread, vinegar, and 2 tsp. salt and blend until puréed, about 2 minutes. The soup should be very smooth; if it’s not, continue blending. Add the olive oil and process a few more seconds to combine. Divide among 6 soup bowls and garnish with basil sprigs, or refrigerate until ready to use.
Make Ahead Tips
The soup can be refrigerated for up to 3 days.
nutrition information (per serving):
Photo: Scott Phillips