Kosher salt

Freshly ground black pepper

Red pepper flakes (optional)

1 large yellow onion, diced

1/4 cup tomato paste

4 cups (32 ounces) low-sodium vegetable broth

Arrange a rack in the middle of the oven and heat to 425 F.

Line a rimmed baking sheet with parchment paper. Remove the whole tomatoes from the cans (reserving the juice), cut them in half if large, and lay them out in a single layer on the baking sheet. Scatter the garlic cloves and thyme sprigs over the tomatoes and drizzle with 1 tablespoon of the oil. Season with salt, pepper and a pinch of red pepper flakes (if using). Roast until soft and caramelized, 30 to 35 minutes.

Meanwhile, heat the remaining 1 tablespoon of oil in a Dutch oven over medium-high heat until shimmering. Add the onion, season with salt and pepper, and saute until translucent and softened, about 5 minutes. Add the tomato paste and saute until the paste has deepened in color, about 2 minutes more. Remove from the heat.

When the tomatoes are ready, discard the thyme sprigs. Transfer the tomatoes and garlic cloves to the pot; add the reserved tomato juice and the vegetable broth. Stir to combine and bring to a boil. Reduce the heat to maintain a gentle simmer, cover the pot, and simmer 20 minutes.

Puree the soup in batches in a stand blender or with an immersion blender until smooth. Season with salt and pepper as needed.

Recipe notes: Leftovers can be stored in an airtight container and refrigerated for up to five days, or frozen for up to three months.

(Sheela Prakash is an assistant food editor for TheKitchn.com, a nationally known blog for people who love food and home cooking. Submit any comments or questions to editorial@thekitchn.com.)