Preheat your oven to 450 degrees F.

On a lightly greased baking sheet, spread out the chopped tomatoes, diced onion, and minced garlic evenly. Drizzle with olive oil and sprinkle with salt and pepper. Roast them in the preheated oven for about 30 minutes until they are soft and slightly charred.

Once roasted, remove the tray from the oven and let it cool slightly. Transfer everything into a blender or use an immersion blender directly in the pot. Add fresh basil during blending and blend until smooth.

In a large pot over medium heat, melt salted butter. Whisk in all-purpose flour to form a roux. Cook this mixture for about two minutes until it turns golden brown.

Slowly pour in the vegetable broth while continuously whisking to prevent lumps. Bring this mixture to a gentle simmer before adding your blended tomato mixture along with granulated sugar.

If you’re looking for an extra creamy finish, stir in heavy cream at this point. Allow everything to simmer gently for another five minutes.