Make the spaetzle dough by whisking together the flour, salt, pepper and nutmeg in a large bowl. In a separate small bowl, beat the eggs with the milk until well combined. Add the egg mixture to the flour, and using a wooden spoon or spatula, gently stir together until you have a sticky dough. Stir in 3 teaspoons of the fresh herbs. Let it sit in the refrigerator while you start the soup. This can even be done the night before.
Start the soup: In a large pot, heat olive oil over medium heat. Add the carrots and celery and cook, 2 minutes. Add the chicken stock, chicken breast and onion, bring to a boil and cook for about 20 minutes, or until the chicken is poached. Remove the onion and discard. Take the chicken out of the pot, and when it has cooled slightly, remove the bone and skin and discard. Shred the chicken and return to the soup. Season to taste with salt and pepper.
Bring a pot of salted water to a boil. Using a spaetzle maker or colander, pass the dough through the holes and drop it into the water. The dumplings will cook quickly and float to the top. Use a slotted spoon to retrieve the spaetzle and transfer it to the soup. If you wish, you can also drop the spaetzle directly into the soup pot. Stir in the remaining teaspoon fresh herbs. Serve the soup immediately.