In a large pot or Dutch oven, heat over medium-high heat and add the Italian sausage. Sear the sausage for 5–7 minutes until it's nicely browned and cooked through, breaking it apart with a wooden spoon as it cooks. Once browned, drain any excess fat from the pot to avoid a greasy soup.

Reduce the heat to medium and add unsalted butter to the pot, allowing it to melt completely. Then, stir in the mirepoix (carrots, celery, and onion) and cook for 5–10 minutes, or until the vegetables soften and the onions become translucent. Add the minced garlic in the last minute to enhance the aroma without burning it.

Next, stir in the chopped baby gold potatoes, dried parsley, and basil, incorporating them well into the sautéed vegetables. Pour in the chicken broth, bringing the mixture to a gentle boil. Once boiling, cover the pot, reduce to low heat, and let it simmer for 15–20 minutes, or until the potatoes are fork-tender and infused with all the savory flavors.

While the soup simmers, create a creamy base by melting the remaining butter in a separate saucepan over medium heat. Whisk in the flour to form a roux, cooking for about 1 minute until it turns golden. Gradually add milk, whisking continuously until the mixture thickens and bubbles, ensuring there are no lumps for a smooth addition to the soup.

Pour the thickened mixture into the soup pot, stirring vigorously to combine everything seamlessly. Add in the shredded extra-sharp cheddar cheese and sour cream, mixing until melted and creamy. Taste the soup, adjusting seasoning with salt and pepper as needed to ensure optimal flavor in your Creamy Sausage Potato Soup.

Finally, ladle the warm soup into bowls, garnishing with fresh herbs if desired for an added touch of color. Serve this delightful Creamy Sausage Potato Soup with hearty buttered bread on the side for dipping.