In a large pot, combine the milk, chicken broth, salt, butter, and mashed potatoes.
Bring the mixture to a boil, stirring occasionally.
Once boiling, gradually add the sifted flour, stirring constantly until a smooth dough forms.
Cook the dough for 5-7 minutes over medium-low heat, stirring until it pulls away from the sides of the pot and forms a ball.
Transfer it to a lightly oiled surface. Let the dough cool enough to handle.
When it cools down enough to handle, knead the dough until it becomes smooth and elastic. Always keep it covered with plastic wrap to prevent it from drying out.