Melt butter in a large pot over medium heat until browned and fragrant.

Add diced celery, carrots, and onion. Cook until softened, about 8-10 minutes.

Stir in minced garlic and cook for 1 minute until fragrant.

Add tomato paste and cook, stirring, for 2 minutes.

Pour in chicken broth, scraping up any browned bits from the bottom of the pot.

Add diced tomatoes (undrained) and tomato sauce. Stir in sugar and bring to a simmer.

Reduce heat to low, cover, and simmer for at least 20 minutes.

Stir in fresh basil leaves just before serving.