Cut the 1 lb sausage into 1-inch pieces.

Heat a pot over medium-high heat. Add 1 Tbsp olive oil and cook the sausage until browned, about 5-7 minutes. Transfer the sausage to a plate and set aside.

In the same pot, add 1 cup chopped onion and 3 minced garlic cloves. Cook for 1 minute.

Stir in 3 cups peeled and chopped russet potatoes, 1 teaspoon Italian seasoning, ½ teaspoon salt, ½ teaspoon ground black pepper, and ¼ teaspoon red pepper flakes. Cook for 3-4 minutes, stirring occasionally. Add a splash of broth if needed to prevent sticking.

Pour in 4 cups beef broth. Bring the mixture to a boil, then reduce the heat and let it simmer for 3-4 minutes. Add the cooked sausage back to the pot. Let everything simmer until the potatoes are tender (test by poking them with a fork), about 5-8 minutes.

Once the potatoes are tender, stir in 2 cups baby spinach and cook for 1-2 minutes until wilted.

Remove the pot from heat and stir in ½ cup freshly grated parmesan. Scoop into bowls and serve warm.