Sauté the finely chopped sweet onion and minced garlic in a large pot over medium heat for about 2-3 minutes until the onions are translucent and fragrant.
Pour in the two cans of diced tomatoes (with their juices) into the pot and stir well to combine.
Add the kosher salt and freshly ground black pepper to the pot and stir to incorporate.
Bring the mixture to a gentle simmer, allowing it to cook for about 5 minutes, stirring occasionally.
Add the fresh basil leaves, stirring them in and letting them wilt for a minute.
Blend the soup using an immersion blender until it reaches your desired level of smoothness.
Return the pot to low heat and stir in the heavy whipping cream, warming it through for an additional minute or two.
Taste the soup and adjust the seasoning if needed.
Ladle the soup into bowls and enjoy hot, garnished with extra basil or a drizzle of cream if desired.