Heat olive oil in a Dutch Oven or soup pot over medium-high heat. Add Italian Sausage (casings removed), chopped onion, garlic, and seasonings.
Cook, breaking up the sausage as you go, until onion is translucent and sausage is fully cooked.
Add chicken broth, half & half, and drained diced tomatoes.
In a separate small saucepan, melt 3 Tbsp. butter over medium-low heat. Stir in 1/4 cup flour and cook, stirring constantly, 3-5 minutes until mixture is bubbly and a thick paste (roux) forms.
Stir the roux into the soup and bring the mixture to a low boil, stirring regularly. Soup will thicken.
Add gnocchi and chopped spinach and lower heat to a simmer. Simmer 5 minutes.
Notes
*For a thinner soup, you can either omit the roux or add 1-2 cups additional chicken broth.