Cook elbow macaroni according to package directions. Drain well; set aside.
Meanwhile, warm broth in large saucepan over medium heat. In separate saucepan, melt butter over medium heat. Add flour and stir, cooking 2-3 minutes. Slowly add hot broth to flour mixture and whisk until smooth. Increase heat to high and bring mixture to boil. Reduce heat to medium and simmer 1-2 minutes, stirring constantly.
Add spinach; cook 3-5 minutes. Remove from heat. Add elbow macaroni and stir. Add cheese, season with salt and nutmeg to taste, stir just a little.
The best thing about this soup is the gooey stings of melted cheese, so don’t over stir, the cheese shouldn’t melt completely, just soften.