Rappie Pie

Preheat oven to 400 degrees F (200 degrees C). Grease a 10x14x2-inch baking pan.

Heat margarine in a skillet over medium heat; stir in onion. Cook and stir until onion has softened and turned translucent, about 5 minutes. Reduce heat to low and continue to cook and stir until onion is very tender and dark brown, about 40 minutes more.

Bring chicken broth to a boil in a large pot; stir in chicken breasts, reduce heat, and simmer until chicken is no longer pink at the center, about 20 minutes. Remove from heat. Remove chicken breasts to a plate using a slotted spoon; reserve broth.

Juice potatoes with an electric juicer; place dry potato flesh into a bowl and discard juice. Stir salt and pepper into potatoes; stir in enough reserved broth to make the mixture the consistency of oatmeal. Set remaining broth aside.