Preheat your oven to 400ºF. Line a baking sheet with parchment paper.
Arrange tomatoes and onion on a single layer on the prepared baking pans. Drizzle with oil.
Roast in the preheated oven for 30 minutes. Add garlic; continue roasting until mixture is tender, about 15 minutes more.
Bring broth to a boil in a large pot over high heat. Reduce heat and simmer, covered.
Meanwhile, put 1/2 of the tomato mixture in a blender, along with half of the white beans. Cover and pulse 3 times, then blend until smooth, adding hot broth as needed. Pour into the pot with broth. Repeat with remaining tomato mixture and white beans, then stir into the pot until combined.
