Rappie pie is a traditional Nova Scotia, Canada dish, made of grated potato, onion, and chicken; with broth served to pour over at the table.
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.