In a large soup pot over medium-high heat, cook the Italian sausage until thoroughly browned, approximately 10 minutes, breaking it apart with a spoon during the process. Once cooked, transfer the sausage to a plate lined with paper towels, retaining about a tablespoon of the rendered fat in the pot. Discard any excess.

Melt the butter in the same pot, then add the diced onion and celery. Sauté for 4 to 5 minutes, stirring occasionally and scraping any caramelized bits from the base.

Incorporate the minced garlic and sprinkle in the flour. Continue to cook for 2 minutes, stirring constantly to eliminate the raw taste of the flour.

Gradually pour in the chicken broth while whisking continuously to ensure the flour dissolves completely, forming a smooth mixture.

Add the half-and-half, Worcestershire sauce, optional red pepper flakes, and diced potatoes to the pot. Return the browned sausage to the mixture. Increase the heat to bring the soup to a boil.

Once boiling, reduce the heat to a gentle simmer (medium-low is ideal), partially cover the pot with its lid, and let cook for about 15 minutes, or until the potatoes are fork-tender and the soup has reached a creamy consistency. Stir occasionally to avoid sticking and to monitor the simmer.

Adjust the seasoning with salt and pepper as needed before serving.