01 -
In a large pot over medium heat, melt unsalted butter. Add celery, fennel, onion, and 1/2 teaspoon salt; cook, stirring occasionally, until vegetables are softened and translucent, 7 to 8 minutes.
02 -
Incorporate tomato paste. Cook, stirring frequently, until paste is darkened and fragrant, about 2 minutes. Add crushed red pepper flakes, stir, and cook for 1 minute.
03 -
Add whole peeled tomatoes with juices, tomato juice, and light brown sugar. Bring to a simmer. Using a wooden spoon or spatula, gently break down tomatoes into large pieces. Cook, stirring occasionally, until slightly reduced, about 10 minutes. Remove from heat and let cool for 5 minutes.
04 -
Transfer half the tomato mixture to a standard blender; blend until smooth. Repeat with remaining mixture, or use an immersion blender directly in the pot until fully pureed.
05 -
Return the soup to the pot. Stir in heavy cream until fully incorporated. Cook over medium heat, stirring frequently, just until warmed through; do not allow to boil. Season with remaining 1 1/2 teaspoons salt.
06 -
Ladle soup into bowls. Drizzle with additional cream and garnish with fresh basil leaves.