4 tablespoons (½ stick) butter
2 tablespoons olive oil
1 medium onion, chopped
coarse salt and ground pepper
¼ cup all-purpose flour
3 tablespoons tomato paste
2 sprigs fresh thyme (or ½ teaspoon dried thyme)
2 cans (14.5 ounces each) reduced-sodium chicken broth
2 cans (28 ounces each) whole peeled tomatoes in juice (with basil if available)
In a 5-quart saucepan or Dutch oven, melt butter over medium heat; add oil and onion, season with salt and pepper. Cook until onion is translucent, about 5 minutes. Stir in flour and tomato paste, cook 1 minute.
To saucepan, add thyme, broth, and tomatoes, breaking up tomatoes with your fingers. Bring to a boil; reduce heat and simmer, 30 minutes. (Remove thyme sprigs before blending.)
Using an immersion blender, purée soup in pot, leaving a fair amount of the tomatoes in chunks. Or, working in several batches, purée half (5 cups) of the soup in a conventional blender until smooth; return to pot. Season with salt and pepper. Serve immediately, or let cool to room temperature before dividing among airtight containers (leaving 1 inch of space at the top) and freezing.