Irish Potato Pie

From 1874 :

Pare and cook done one half gallon potatoes, then mash and pass through a sieve. To every ½ lb. potatoes add ½ lb. sugar, same of butter, 3 eggs, 1 pint cream; bake without upper crust.
When baked one can add much to the appearance of the pie by mixing the froth of one egg with one tablespoonful white sugar, and spreading it on the top; then return to the oven till slightly browned.