Saute onion and garlic in oil. Deglaze with a little chicken broth as bottom of pan darkens. Remove to a bowl. In same pan, saute sausage, breaking up. Add tomatoes and remaining chicken broth. When reduced by one-half, sprinkle flour and stir. When thickened, stir in half-and-half. Reduce just a little more, stir in parmesan, if desired, then serve over pasta