Step 1

Preheat oven to 450 degrees. Toss together tomatoes, onions, garlic and oil; season with salt and pepper. Arrange vegetables in a single layer on a rimmed baking sheet and bake until tomatoes are deep brown in spots and onions are soft, 45 minutes.

Step 2

Transfer vegetables and all juices to a large dutch oven or heavy pot. Add chicken broth and bring to a rapid simmer. Cook until slightly reduced, about 25 minutes.

Step 3

Transfer soup to a large bowl. In batches, fill blender halfway with soup, puree until smooth, transferring to pot as you work (use caution when blending hot liquids). Stir in tarragon and season with salt and pepper. If necessary thin with additional chicken broth. Serve with a drizzle of olive oil.