Lemon-Herb Turkey Meatballs with Caramelized Onion Sauce

In a large bowl, combine 2 lbs ground turkey, 1 cup panko breadcrumbs, 2 beaten eggs, 3 minced garlic cloves, 1/2 cup chopped parsley, 2 tablespoons chopped thyme, 1 tablespoon chopped rosemary, 2 tablespoons lemon zest, 2 tablespoons lemon juice, 1 1/2 teaspoons salt, and 1/2 teaspoon black pepper. Mix gently until just combined, being careful not to overmix.

Form the mixture into 24 meatballs, about 2 inches in diameter. Place on a baking sheet lined with parchment paper and refrigerate for 15 minutes to firm up.

While meatballs are chilling, bring a large pot of salted water to boil for the pasta.

Heat 2 tablespoons olive oil in a large, deep skillet over medium heat. Working in batches if necessary, cook the meatballs until browned on all sides and cooked through, about 8-10 minutes total. Transfer to a plate and cover to keep warm.

In the same skillet, add the remaining 2 tablespoons olive oil. Add 4 large thinly sliced yellow onions and cook over medium-low heat, stirring occasionally, until they begin to soften, about 10 minutes.

Add 2 tablespoons brown sugar, 1/2 teaspoon salt, and 1/2 teaspoon black pepper to the onions. Continue cooking, stirring occasionally, until onions are deeply caramelized, about 15-20 minutes.

Add 3 remaining minced garlic cloves to the caramelized onions and cook for 1 minute until fragrant.

Add 3 tablespoons balsamic vinegar to the skillet and scrape up any browned bits from the bottom. Cook until vinegar is mostly evaporated, about 2 minutes.

Pour in 2 cups chicken broth and 1 tablespoon lemon juice, bring to a simmer. In a small bowl, mix 1 tablespoon cornstarch with 2 tablespoons water, then stir into the sauce. Simmer until slightly thickened, about 3-4 minutes.

While the sauce is simmering, cook 1 lb fettuccine pasta according to package directions until al dente. Reserve 1 cup of pasta water before draining.

Return the meatballs to the skillet with the sauce, gently stirring to coat. Simmer for 5 minutes to reheat the meatballs and allow flavors to meld.

In another large skillet, melt 2 tablespoons butter over medium heat. Add 6 cups baby spinach and 2 cups halved cherry tomatoes. Sauté until spinach is wilted and tomatoes begin to soften, about 3-4 minutes. Season with salt and pepper to taste.

Toss the drained pasta with the spinach and tomato mixture, adding a splash of reserved pasta water if needed to loosen.

Serve the meatballs and caramelized onion sauce over the pasta. Sprinkle with 1 cup grated parmesan cheese and garnish with additional fresh herbs if desired.