Cook the sausage and red pepper flakes in a heavy pot over medium-high heat until crumbly, bronwed and no longer pink. Drain and set aside.
Cook the bacon in the same pot over medium heat until crisp. Drain, leaving a few tablespoons of drippings with the bacon in the pot. Stir in the onions and garlic, cook until onions are soft and translucent, about 5 minutes.
Pour the chicken broth into the pot with the bacon and onion mixture; bring to a boil over high heat. Add the potatoes, and boil until fork tender. Reduce the heat to medium and stir in the heavy cream and the cooked sausage; heat through. Mix the spinach with the soup just before serving.