Brown the Italian sausage in a cast-iron Dutch oven or large pot. Drain the fat and set the sausage aside.
Using the same pot, melt the butter over medium heat. Add the diced onions carrots, and celery. Saute for 3-4 minutes. Add the minced garlic and saute for 1-2 minutes.
Sprinkle with flour and cook for 1-2 minutes, stirring constantly. Stir in the chicken broth, cooked Italian sausage, kosher salt, coarse-ground black pepper, and bay leaf, and bring to a boil. Turn the heat to low and simmer for 15 minutes, stirring occasionally. Discard the bay leaf.
Stir in the cooked gnocchi and baby spinach. Stir until the spinach wilts a little, and then stir in the half-and-half. Cook on low for 7-10 minutes, stirring occasionally, until heated through.