Heat a large pot over medium-high heat. Add sausage and let it sear for 1 minute, then use a wooden spoon to crumble it. Cook until sausage is deeply browned. Transfer to a plate lined with paper towels, leaving about 1 tablespoon grease in the pot. If there’s not enough grease, add 1 tablespoon olive oil.

In the same pot, melt 1 tablespoon butter. Add diced carrots, celery, and onion. Sauté for 5–7 minutes (or 7–10 minutes if the veggies are larger). Add garlic and cook for 30 seconds more.

Stir in chopped potatoes, dried basil, dried parsley, salt, and pepper. Pour in chicken stock, bring the mixture to a boil, then reduce heat to medium-low. Cover pot and cook for 15–20 minutes or until potatoes are fork-tender.

While potatoes cook, melt 4 tablespoons butter in a separate medium pot over medium heat. Stir in flour and cook, whisking constantly, for 1 minute. Slowly pour in milk, whisking constantly until smooth. Cook, continuing to whisk, until the mixture thickens and gently boils. Stir in heavy cream, then remove from heat.

Once veggies are tender, stir in the milk/cream mixture. Turn off heat and add shredded cheese, a handful at a time, stirring gently until melted. Stir in sour cream, then return the sausage to the soup. Adjust seasoning with salt and pepper to taste.

Serve the soup warm with hearty buttered bread, if desired.