Sauté Aromatics: Melt butter in a 3-quart saucepan over medium heat. Add onion; cook and stir until softened and translucent, 3-5 minutes.
Simmer Soup: Add celery, carrots, broth and rice. Bring to boil; reduce heat and simmer 10-12 minutes, until rice is tender, but still has a little bite.
Mix Gremolata: Meanwhile, zest lemon into a small bowl and add minced parsley and garlic; stir to combine. Juice lemon half into separate small bowl. Set both bowls aside.
Finish and Serve: When rice is tender, add turkey meat; cook and stir until heated through, 2-3 minutes. Stir in reserved lemon juice and season to taste with salt and freshly ground black pepper. Ladle soup into bowls and garnish with parsley mixture. Serve.
Video
Notes
Stock: This soup is good with store-bought broth, but it's fantastic with homemade turkey stock. I've included my method in the post above—it's my favorite way to get every last bit of flavor from the holiday.
Rice: I personally don't rinse the rice because I like how the starch gives the soup a little more body. If you want a really clear, broth-forward soup, give the rice a good rinse in a fine-mesh strainer before you add it to the pot.
Storage: Leftovers will keep beautifully in the fridge for up to 4 days. Just know that the rice will continue to drink up the broth, so the soup will get thicker. Simply add another splash of broth when you reheat it. You can also freeze the soup for up to 3 months. If you're planning to freeze some or all of it, be sure to rinse the rice before adding to the soup.