Preheat the oven to 350 degrees. Mix Italian sausage, egg, bread crumbs, and parmesan cheese (and salt and pepper, if wanted). Mix until well combined. Form into 1 inch diameter meatballs. Place on a foil lined baking sheet and bake for 30 minutes, until cooked through.
Meanwhile, begin to prep the orzo. Heat the olive oil in a deep saucepan over medium-high heat. Once hot, add onion, celery, and carrots. Cook until softened, about 5-8 minutes.
Add the butter and garlic. Once the butter has melted, add the orzo and toast for 4-5 minutes, stirring often.
Add the chicken stock in half cup increments, stirring very often. Once each ½ cup has been absorbed, add the next ½ cup, cooking about 15-18 minutes, until the orzo is al dente. (Think risotto)
Add just a bit more stock and stir in the spinach, parmesan cheese, and pepper. Cook until the spinach is wilted. Plate the orzo and top with baked meatballs.