In a large pot over medium heat, cook 1 pound ground Italian sausage, breaking it apart, until browned and fully cooked. Drain any excess grease.
Add ½ chopped onion to the pot with the sausage and cook for 3 to 4 minutes until softened. Stir in 1 tablespoon minced garlic and cook for about 30 seconds until fragrant.
Slowly pour in 4 cups chicken broth, stirring and scraping the bottom of the pot to release any browned bits for added flavor.
Stir in 4 Russet potatoes, peeled and diced, along with 1 teaspoon salt and 1 teaspoon pepper. Bring the mixture to a boil, then reduce the heat to a simmer.
Cook uncovered for 20 to 25 minutes until the potatoes are fork tender.
In a small bowl, whisk together 1 cup heavy whipping cream and 2 tablespoons cornstarch until smooth.
Stir the cream mixture into the soup and cook for a few minutes until the soup thickens.
Serve warm topped with ¼ cup parmesan cheese.
Notes
Refrigerate the leftovers in an airtight container for up to 5 days.