In a large bowl mix one egg with the mashed potatoes.
Next, add the flour to the mixture and knead until a dough is formed.
Now grease a pan with some oil and wait until it's heated.
Take half of the dough and place it in the pan, in a circular shape. On the dough, place your chosen fillings and wait until the dough is golden brown from the bottom.
Then, place the other half of the dough on top and flip it to cook from both sides. When the bottom is golden brown, your mashed potato pie is ready to serve!