Place tomatoes, pepper, cucumber, onion (if using) and garlic in blender and pulse a few times.
Add sherry vinegar.
Blend on high two minutes
Slowly stream in olive oil while blender is running.
Taste for salt, vinegar and oil balance and adjust before you proceed to the next step.
Strain soup into a large bowl to catch all the solids. Use a rubber spatula to press mixture through strainer.
Discard solids.
Chill soup 6-8 hours or overnight. (Overnight is better)
Serve cold with a drizzle of olive oil and chopped basil (optional)
Serve in glasses, over ice if desired, or in a bowl with a few drops of olive oil on top.
Any leftovers stay refrigerated for a couple of days with very slight separation that a quick stir won’t fix.