In a medium bowl, mix together flour, salt, and baking powder. Stir in mashed potatoes and onion until thoroughly combined. In a separate bowl, whisk together eggs and milk, and stir lightly into potato mixture.
Stir in corn syrup and nutmeg, mixing well. Heat a large griddle to medium-high heat. Coat with shortening and spoon potato mixture onto griddle in 12 equal portions. Fry until brown on both sides. Serve hot.