In a large pot over medium heat, cook the sausage until browned, breaking it apart as it cooks. Remove and set aside.
In the same pot, add olive oil and sauté the onion until translucent, about 4–5 minutes.
Add garlic and cook for 30 seconds. Stir in the flour and cook for 1 minute, stirring constantly.
Gradually whisk in chicken broth and heavy cream. Add potatoes, Italian seasoning, red pepper flakes, salt, and pepper.
Bring to a boil, then reduce to a simmer and cook until potatoes are tender, about 12–15 minutes.
Return the sausage to the pot, stir in spinach or kale, and cook until wilted.
Remove from heat and stir in shredded cheese until melted and smooth.
Serve hot with crusty bread or your favorite crackers.