Brown the Sausage: Heat a large pot over medium-high heat. Add the Italian sausage and sear for 1 minute before crumbling. Cook for 5-7 minutes until browned. Remove the sausage, leaving some grease behind.

Sauté the Vegetables: In the same pot, melt 1 tablespoon of butter. Add the mirepoix and sauté for 5-10 minutes until softened. Stir in minced garlic and cook for another 30 seconds.

Add Potatoes and Stock: Stir in chopped potatoes, parsley, basil, salt, and pepper. Pour in stock and bring to a gentle boil. Reduce heat to medium-low, cover, and simmer for 15-20 minutes until potatoes are tender.

Make the Creamy Base: In a separate pot, melt 4 tablespoons of butter and whisk in flour. Gradually add milk while whisking, cooking for 3-5 minutes until thickened. Stir in heavy cream and remove from heat.

Combine and Finalize the Soup: Once potatoes are tender, pour in creamy mixture along with cheddar cheese, stirring until melted. Add the browned sausage back into the pot, taste and adjust seasoning.

Serve and Enjoy: Ladle soup into bowls, serve warm with a dollop of sour cream and buttered bread if desired.