In a large pot over medium-high heat, cook the Italian sausage, breaking it apart as it cooks for about 5–7 minutes until browned. Transfer to a plate, leaving drippings in the pot.

In the same pot, sauté the mirepoix in the reserved grease for about 4–5 minutes until softened. Add the minced garlic and sauté for an additional minute.

Stir in the baby gold potatoes, dried parsley, and basil, seasoning with salt and pepper. Toss for about 2 minutes.

Pour in the chicken stock, increase heat to high, bring to a boil, then reduce heat and simmer for 15–20 minutes until the potatoes are tender.

In a separate pot, melt the butter, whisk in flour and cook for about 1 minute. Gradually add milk, whisking until thickened, then stir in heavy cream off the heat.

Pour the creamy mixture into the soup pot, stir until combined. Add the sausage and cheddar cheese, stirring until melted. Adjust seasoning if necessary.

Ladle the soup into bowls, top with sour cream, and serve warm.