Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9×13 inch pan. Bring a small pot of water to boil, add potato and let it boil until tender (approximately 10 minutes). Drain well, then mash. Set aside 1 cup.
Sift together the flour, baking powder and salt. Stir in the blueberries to coat them in the flour mixture. Set aside.
In a large bowl, cream together the shortening and sugar until light and fluffy. Mix in the warm mashed potato. Beat in the eggs one at a time, then stir in the vanilla. Stir in the flour mixture with the blueberries, mixing just until incorporated.
Pour batter into prepared pan. Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow to cool.
