Step 5) Add the chicken stock and let it come to a gentle boil.
Step 6) Reduce heat to low, cover, and let simmer for 5–10 minutes.
Step 7) Meanwhile, in a large bowl, combine the ground chicken, egg, breadcrumbs, onion, garlic, salt, and pepper. Lightly mix all the ingredients until everything is combined. (Do not overmix as this tends to make the meatballs tough.)
Step 8) Moisten hands with water and form round meatballs no larger than a golf ball.
Step 9) Bring the temperature of the sauce to a simmer, then very carefully place the meatballs in the sauce and cook, covered, for about 15 minutes (do not stir as the meatballs will break apart).
Step 10) Uncover and add the capers and olives (if using).
Step 11) Cook, uncovered, for another 10 minutes
Step 12) Taste and adjust seasoning. Top with fresh cilantro (if using).