Combine mashed potatoes, shortening and egg yolks in a bowl. In another bowl mix flour, salt and cream of tarter. Add flour mixture to mashed potato mixture a small amount at a time, alternating with the water. Cover with plastic wrap and let stand 10 – 15 minutes.

Roll out dough to about 1/8th of an inch thick, cut with a 3 inch round cookie cutter.

Place about 1 heaping teaspoon of filling on each round, then fold and pinch edges together.

To cook, bring a large pot of water to a boil. Add perogies in batches to boiling water and cook just until they float and puff slightly. (about 5 minutes)

Remove from water. Perogies can be served at this point, or fried in a pan with oil (and I add a bit of butter) until golden brown.