Preparation / Directions:
Turn mashed potatoes into a large bowl. Add flour, salt, and onion. Mix thoroughly with hands and fingers until completely mixed and smooth. Pat on a lightly floured board until 1/2 inch thick. Cut with a 3-inch cookie cutter. Place on a cookie sheet, cover lightly with waxed paper, and chill in refrigerator until just before cooking. To cook, use 1 tablespoon margarine at a time. Melt margarine in a large frying pan or stovetop griddle. Fry cakes over moderately hot heat, turning to brown on both sides. Serve immediately.
Certain Irish folk refer to potato cakes as "praties". They are great! Mix and shape ahead, then chill them before cooking.