Combine all meatball ingredients in a large bowl. Mix until just combined. Do not overwork the meat. Cover and refrigerate for 15-20 minutes to firm up slightly.
Bring the chicken stock to a gentle simmer in a wide pot with the olive oil, salt, bay leaf, and white pepper.
Wet your hands slightly. Roll the meat mixture into walnut-sized balls (about 30-35g each), making 20-24 total. Lower them gently into the simmering broth one by one. Do not stir for the first 5 minutes.
Cover the pot loosely and simmer on medium-low heat for 30-35 minutes, turning the meatballs once halfway through. Taste and adjust salt.
Whisk the eggs until light and frothy, about 1-2 minutes. Add the lemon juice and whisk to combine. Ladle two full ladles of hot broth (no meatballs) very slowly into the egg-lemon mixture while whisking constantly. This tempering step prevents the eggs from scrambling.
Remove the pot from heat entirely. Pour the tempered avgolemono back into the pot in a slow, steady stream, gently swirling. The broth will turn silky and lemon-cream in colour. Do not return to heat. Taste, adjust seasoning, and serve immediately.