In a Dutch oven, cook sausage and onion over medium heat, until sausage is no longer pink, breaking the sausage into crumbles as it cooks. Drain grease.
Return the sausage mixture to the Dutch oven and add the garlic. Cook for 1-2 minutes more, or until garlic is fragrant. Stir in the flour.
Gradually add the broth, stirring constantly, until slightly thickened. Stir in the milk and bring to a boil. Add the potatoes and simmer for 10-15 minutes, or until potatoes are tender.
Stir in the spinach and cream and return to a simmer. Season with salt and pepper, to taste, before serving.
