In a large pot over medium heat, cook ground Italian sausage, breaking it apart, until browned and fully cooked. Drain any excess grease.
Add chopped onion to the pot with the sausage and cook for 3 to 4 minutes until softened. Stir in minced garlic and cook for about 30 seconds until fragrant.
Slowly pour in chicken broth, stirring and scraping the bottom of the pot to release any browned bits for added flavor.
Stir in Russet potatoes, peeled and diced, along with salt and 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 heavy whipping cream and cornstarch until smooth.
Stir the cream mixture into the soup and cook for a few minutes until the soup thickens.
Serve warm topped with parmesan cheese.
Notes
Refrigerate the leftovers in an airtight container for up to 5 days.