Add the chicken stock, bouillon, chicken breast, onion, carrots, and celery to a large pot over medium-high heat.

Bring it to a boil, then reduce heat to a simmer and cover. Let it simmer for 20 minutes.

Remove the chicken and set aside. Discard the onion.

Combine the flour, baking powder, salt, and buttermilk in a large bowl. Stir until a dough forms.

If the dough is too dry, add a little more buttermilk; if it is too wet, add a little more flour.

Dust the dough heavily with more flour.

Roll the dough out thinly and slice it into squares.

Add the dumplings to the simmering stock, stirring gently to prevent sticking.

Cover and let the dumplings cook for another 20 minutes to let the stock thicken.

Meanwhile, shred the chicken.

Once the dumplings are done, return the chicken to the pot and stir to combine. Stir in the milk, then turn the heat off and let the chicken and dumplings sit for 5 minutes before serving.