Place chicken in a large pot.

Cover with water and bring to a boil.

Add chopped onion, carrots, and celery.

Simmer slowly until chicken is tender (2.5-3 hours).

Remove chicken and debone, then chop into small strands.

Set aside chopped chicken.

Save 1/2 cup of chicken broth and let cool.

Puree the cooked vegetables with an immersion blender (or strain and puree in a regular blender).

Return pureed vegetables and broth to the pot.

Season broth with butter, salt, and pepper to taste.

Bring to a boil.

Prepare the dumpling dough.

In a mixing bowl, cut shortening into flour.

Stir in the cooled chicken broth.

Cover and let stand for 30 minutes.

Roll out dough as thinly as possible on a floured surface.

Cut into strips or small squares.

Drop layers of dumplings into the boiling broth, allowing the broth to boil over each layer before adding more.

Do not stir.

Cover and cook for 12 minutes.

Carefully add the chopped, deboned chicken to the pot.

Serve hot.