Heat olive oil in a large pot over medium heat. Add the onions and stir until soft. About 4-5 minutes. Stir in the garlic and pepper flakes, cook for 1 minute.
Carefully pour in white wine, simmer until almost completely evaporated. Pour in the cans of tomatoes with their juices, chicken broth and basil. Increase heat to medium-high and bring soup to a boil for 1 minute. Then, reduce heat and simmer soup for 10 minutes.
Working carefully, puree soup with a hand blender until completely smooth. Or, scoop it into a blender and puree until smooth. When all of the soup is completed return it to the pot and bring it to a simmer.
Allow soup to simmer for a few minutes, then stir in the sugar and vinegar. Stir in spinach and allow to wilt. Serve hot with a garnish of cheese.
Notes
Need to drain the water from your thawed spinach? Put it in a potato ricer and squeeze until excess water is drained! This soup freezes well, simply put it in a sealed container until you want to eat it.