1. Preheat oven to broil with rack 9 inches from heat. Combine pork, panko, 1/3 cup Parmigiano-Reggiano cheese, parsley, egg, 2 teaspoons chopped garlic, salt, and pepper in a medium bowl. Mix gently with hands until just combined.
2. Roll mixture into 20 meatballs (about 2 tablespoons each). Place meatballs 1 inch apart on a broiler-safe baking sheet lined with aluminum foil.
3. Broil until browned and cooked through, 6 to 9 minutes. Set cooked meatballs aside at room temperature until ready to serve.
4. Combine stock and 2 cups water in a medium saucepan; bring to a simmer over medium. Reduce heat to medium-low.
5. Heat oil and 2 tablespoons butter in a large saucepan over medium. Add onion, celery, and remaining chopped garlic; cook, stirring often, until softened, about 5 minutes.
6. Add rice and cook, stirring constantly, until translucent, 1 to 2 minutes.
7. Add wine and cook, stirring often, until almost completely reduced, 1 to 2 minutes.
8. Add 1 cup warm stock mixture and cook, stirring constantly, until most of the liquid has been absorbed.
9. Add remaining stock mixture, 1 cup at a time, stirring until liquid has been absorbed after each addition, until rice is al dente, about 20 minutes.
10. Remove from heat. Stir in remaining cheese and remaining 2 tablespoons butter. Stir in spinach; cook, stirring occasionally, until just wilted, about 30 seconds.
11. Divide risotto and meatballs among bowls. Drizzle with oil; garnish with additional cheese, parsley, and pepper.
