In a large, deep pot, place chicken and cover completely with water. Add salt & pepper to taste. Set pot on the stove and cook at medium-high heat for up to 2 hours, adding more water as needed to keep the chicken covered.
Remove chicken from pot and set aside on a plate to cool. Leave chicken broth in the pot on the stove and turn the heat down to low to simmer while making dumplings.
In a mixer bowl, add flour, baking powder, salt, pepper & crushed red pepper flakes. Sift together with a whisk. Add shortening and cut into the flour using a pastry blender or two forks until the mixture is crumbly.
Add the milk to the flour, 1/2 a cup at a time, stirring thoroughly with the paddle attachment on low or with a wooden spoon until the milk is incorporated and the dough is formed.
Dump dough out onto a parchment paper lined countertop and roll out to a 1/2 inch thickness. (You can place another sheet of parchment paper over the top of the dough while rolling for easy cleanup and smooth rolling).
Turn the simmering chicken broth up to medium-high, so that its really boiling. Cut dough into 2x2 inch squares and drop them into the boiling broth. Repeat with all of dough.
While dough is cooking, begin deboning the chicken. As you remove chicken from bones, break up the pieces and add them to the cooking pot. Discard bones.
Turn heat down on pot to low and let simmer for up to an hour, stirring often so that the bottom doesn't burn.