Heat 1 tablespoon of olive oil in a large saucepan over medium heat.
Cook and stir 1 large chopped onion and 3 minced garlic cloves in hot oil until fragrant, about 2 to 3 minutes.
Pour vegetable broth over the onion mixture.
Add 2 cans of fire-roasted diced tomatoes, 1 tablespoon chopped cilantro, 1 teaspoon white sugar, and 1/4 teaspoon red pepper flakes to the saucepan.
Bring the mixture to a boil, then reduce heat to medium-low.
Place a cover on the saucepan and simmer until the tomatoes are really soft, about 15 minutes.
Pour the tomato mixture into a blender, filling no more than half full.
Cover and hold the lid in place, pulse a few times before leaving on to blend.
Puree the mixture in batches until smooth and return to the saucepan.
Put the pureed soup over medium heat and cook until hot, about 5 minutes.
Stir in the remaining 1 tablespoon chopped cilantro and 1/2 cup heavy whipping cream into the soup.