Season chicken thighs or breasts with kosher salt, black pepper, and red pepper flakes if using
Heat olive oil in a large pot over medium-high heat
Add chopped carrots, celery, and onion, and sauté until softened
Add minced garlic and cook until fragrant
Pour in chicken broth (or broth and water mixture) and bring to a boil
Add seasoned chicken and Parmesan rind if using, and simmer until chicken is cooked through
Remove chicken from pot and shred or cut into bite-sized pieces
Add dried farro to the broth and cook until tender
In a bowl, whisk together eggs and egg yolk
Temper the eggs by slowly adding hot broth to the egg mixture while whisking constantly
Pour the tempered egg mixture back into the pot while stirring gently to create a silky broth
Return shredded chicken to the pot
Add baby spinach and stir until wilted
Finish with lemon juice to taste
Garnish with fresh dill or parsley and freshly grated Parmesan before serving
