Preheat the oven to 420ºF.
Roast: Transfer the tomatoes, garlic, and onion to a large casserole or baking dish. Toss with a drizzle of olive oil, and a dash of salt. Roast for 35 minutes or until the tomatoes have softened, and the onion is golden brown.
Transfer the tomatoes and onion to a large nonreactive saucepan (ceramic or stainless steel), or to a blender.
Blend: Squeeze the garlic cloves from their skin into the saucepan along with any juice or oil remaining in the baking dish. Add the beans, vegetable broth, tomato paste, maple syrup, nutritional yeast, and basil. Blend using an immersion blender (or a blender) until smooth. (Transfer to a large saucepan if using a blender.)
Season: Cook over medium-high heat until warmed through, adding more broth, and seasoning as desired. Add oat milk for a creamier texture as needed (optional).
Garnish with chiffonade of fresh basil for serving.
