In a skillet over medium-high heat, cook the bulk Italian sausage until it is browned and broken into small pieces, which should take around 7 minutes. Once done, place it in a bowl to drain.

Dispose of the excess grease from the skillet using a paper towel. Next, melt the butter in the skillet over medium heat. Add the chopped onion and sauté until it becomes translucent, roughly between 2 to 3 minutes. Include the minced garlic and sauté until it releases a fragrant aroma, which should take about a minute.

Whisk in the flour with the melted butter in the skillet for about a minute. Gradually add the unsalted chicken broth and heavy cream, whisking the mixture until it reaches a boil. Lower the heat and let it simmer, stirring occasionally, until it thickens, usually around 10 minutes.

Add the browned sausage back to the skillet. Incorporate the potato gnocchi, chopped spinach, and diced tomatoes. Raise the heat to medium and cook for another 2 to 3 minutes, until the gnocchi is well heated. Season with salt and pepper to your preference.

To serve, sprinkle grated Parmesan cheese over the top.