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

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

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

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

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

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