Peel and cube the sweet potatoes.
Place in a medium saucepan and add the orange juice. Add water to just cover. Season with salt and bring to a boil. Cook until tender, about 20 minutes.
Drain, mash and cool for 10 minutes.
Preheat oven to 350 degrees Fahrenheit.
Heat the oil in a small frying pan and sauté diced onion until golden, stirring frequently. Add onions to the sweet potatoes. Add the mayonnaise, eggs and potato starch. Mix well and season to taste with salt and pepper.
Spread the mixture into an eight- by nine-inch square baking dish.
Bake for 30 minutes or until top is set.
Mix two cups of the potatoes with oil and broth. Add egg and season to taste with salt and pepper.
Place the potato mixture into a piping bag fitted with a large star tip. Pipe the potato mixture across the top of the pie in a pretty design.
Return the pie to the oven for an additional 30 minutes.
Brush oil over the lattice and bake for 10 minutes longer, until golden. Remove from the oven and serve hot.
This dish can be made ahead of time and frozen.