Place the broken-up turkey carcass into a large stockpot. Add the quartered onions, chopped celery, chopped carrots, smashed garlic, fresh thyme, bay leaves, peppercorns, and apple cider vinegar.

Pour in enough cold water to cover everything by at least 2 inches (about 12 cups). Bring to a boil over high heat, then immediately reduce the heat to a very gentle simmer — you want just a few lazy bubbles breaking the surface.

During the first 20–30 minutes, skim off any gray foam that rises to the top using a large spoon or ladle. This is impurities releasing from the bones and skimming them off ensures a clean, clear broth.

Continue simmering uncovered (or partially covered) for 3–4 hours. The longer you go, the richer and more gelatinous your broth will be.

Remove from heat and let cool slightly. Using tongs, pick out and discard the large carcass pieces. If any meat is clinging to the bones, pull it off and set aside — this will go into the soup. Strain the broth through a fine mesh strainer or cheesecloth-lined colander into a large bowl or second pot. Discard the spent vegetables and bones. You should have approximately 10–12 cups of rich golden broth. Season with salt to taste. For best results, refrigerate overnight and skim the solid fat from the surface before using.

In a large soup pot or Dutch oven, heat the olive oil over medium heat. Add the diced onion, sliced celery, and sliced carrots. Sauté for 6–8 minutes, stirring occasionally, until the vegetables are beginning to soften and the onion is translucent.

Add the minced garlic and fresh thyme and cook for another 60 seconds until fragrant, stirring constantly so the garlic does not brown.

Pour in the strained turkey broth (all 10–12 cups). Increase the heat to medium-high and bring to a gentle boil, then reduce to a simmer.

Add the shredded turkey to the pot. Simmer for 15–20 minutes until the carrots are tender when pierced with a fork. Taste and adjust seasoning with salt and pepper.

If using, stir in the baby spinach and cook for 1–2 minutes until just wilted.

While the soup simmers, cook the egg noodles in a separate pot of well-salted boiling water according to package directions. Drain and set aside. Do not add them directly to the soup pot — this prevents them from absorbing all the broth and becoming mushy in leftovers.

To serve, place a generous portion of cooked egg noodles into each bowl. Ladle the hot soup over the top, making sure each bowl gets plenty of turkey, carrots, and celery. Garnish with freshly chopped parsley and an extra crack of black pepper. Serve immediately.