Rustic Vegetable and Polenta Soup

Name: Rustic Vegetable and Polenta Soup
Ingredients: 3 tablespoons extra-virgin olive oil; 2 medium carrots, peeled and diced into 1/2-inch pieces; 1 medium onion, chopped; Kosher salt and freshly ground black pepper; 2 tablespoons chopped fresh flat-leaf parsley; 2 tablespoons chopped fresh thyme; 3 cloves garlic, peeled and smashed or chopped; 3 plum tomatoes, diced into 1/2-inch pieces; 2 medium zucchini, diced into 1/2-inch pieces; 4 cups low-sodium chicken broth; 1/3 cup instant polenta, such as Gia Russa; 3 tablespoons unsalted butter, at room temperature