1-First, prepare by washing and dicing all your vegetables, as this mise en place streamlines cooking. For the stovetop version, heat 1 Tablespoon oil in a large soup pot over medium-high heat. Once hot, add the finely diced carrots (about 1 cup), onion (about 1 cup), and celery (about 1 cup), and sauté for a few minutes until softened.

2-Next, add 2 cans (14.5 ounces each) of diced tomatoes with juice, 2 Tablespoons tomato paste, 4 cups chicken broth, 1 teaspoon oregano, and 1 1/2 teaspoons dried basil leaves. Bring the mixture to a gentle boil and cook until the vegetables are tender, which takes about 10-15 minutes.

3-Then, puree the soup until smooth using an immersion blender or a regular blender in batches. Return it to the pot. In a separate pot, melt 1/2 cup butter over medium-low heat and stir in 1/2 cup all-purpose flour, whisking constantly for about 10 minutes until the roux turns golden brown.

4-After that, add a ladle of the soup to the roux to make a thick paste, then slowly incorporate 2-3 more cups of warm soup while whisking until smooth. Stir this mixture back into the main pot. Finally, add 1 cup parmesan cheese, 1 1/2 cups half and half or whole milk, 1 teaspoon salt, 1/4 teaspoon pepper, and 1/4 cup chopped fresh basil, cooking for a few more minutes until warmed through.

5-For the slow cooker version, start by adding 2 cans of diced tomatoes, the diced carrots, onion, celery, tomato paste, chicken broth, oregano, and dried basil to the slow cooker. Cook on low for 5-6 hours. About 30 minutes before it’s done, prepare the roux as above, then mix it into the soup and puree until smooth. Stir in the cheese, cream, and seasonings, and cook for another 20-30 minutes.