Add the diced tomatoes, finely chopped onion, minced garlic, basil leaves, kosher salt, and black pepper to a blender or food processor.
Pulse or blend until the mixture is smooth and well combined.
Pour the blended tomato mixture into a medium saucepan and set over medium-low heat.
Stir in the heavy whipping cream (or half & half) until incorporated.
Cook, stirring occasionally, for about 5 minutes or until the soup is hot. Adjust seasoning if needed, then serve warm.